Introduction to the estuary, its management and monitoring

The Derwent estuary lies at the heart of the Hobart metropolitan area and is a waterway of great natural beauty and diversity. Named after the Celtic word ‘clear water’ in 1794, the Derwent is an integral part of Tasmania’s cultural, economic and natural heritage. The estuary is an important and productive ecosystem and supports a wide range of habitats and species.

Introduction

Approximately 43% of Tasmania’s population — 221,000 people — live around the estuary’s margins. The Derwent is widely used for recreation, boating, fishing, marine transport and industry. Further upstream, the River Derwent supplies the majority of the region’s drinking water and is a major source of hydroelectric power.

A number of environmental issues affect the Derwent estuary, in particular:

  • heavy metal contamination
  • poor recreational water quality at some bays and beaches
  • low oxygen levels in the upper estuary during summer
  • elevated nutrient concentrations
  • environmental flows and barriers
  • introduced marine pests and weeds
  • loss of habitats and species
  • impacts of climate change, e.g. sea level rise, erosion and habitat loss

Although there have been significant improvements in the treatment of sewage and industrial wastes over the past decade, the Derwent still faces a number of environmental challenges. A strategic and coordinated planning approach across all levels of government, industry and the community is our best hope for a clean and healthy estuary in the future.

Reflections on the River Derwent, New Norfolk.

Image: Tourism Tasmania / Rob Burnett

Management and restoration

The Derwent Estuary Program (DEP) was established in 1999 as a partnership to restore and protect the Derwent estuary. The program has been successful in bringing together a wide range of stakeholders — firstly to build a common understanding, vision and management framework — and secondly to progressively implement this vision through partnership agreements and practical actions.

The program was initially designed to address environmental quality issues such as industrial and urban water pollution, contaminated sediments, invasive species and loss of estuarine ecosystems. More recently, our scope has broadened to include the catchment and channel influences, as well as education and amenity. Key program areas include environmental monitoring and reporting, coordination of regional activities, stormwater management, heavy metal investigations, wetland and seagrass conservation, and promotion of walking tracks.

Our program partners

The DEP, a not-for-profit company limited by guarantee, is supported by the Tasmanian Government, six councils that border on the estuary (Brighton, Clarence, Derwent Valley, Glenorchy, Hobart and Kingborough Councils) and five business partners (Nyrstar Hobart, Norske Skog Boyer, TasWater, TasPorts and Hydro Tasmania).

Other project partners include the Institute of Marine and Antarctic Studies, University of Tasmania, CSIRO, NRM South and BirdLife Tasmania.

Nyrstar Hobart Smelter with rainbow.
Nyrstar Hobart Smelter with rainbow.

Image: Derwent Estuary Program

Tasman Bridge, Hobart.
Tasman Bridge, Hobart.

Image: Derwent Estuary Program

Environmental monitoring and reporting

A fundamental requirement for effective natural resource management is an on-going and reliable source of environmental data. This principle forms the basis of the DEP’s cooperative monitoring program between the state government, councils, industries and research institutes. Formerly independent monitoring programs are now coordinated so as to provide better information on the estuary as a whole, and to report annually on environmental conditions and trends in the Derwent.

This ‘Report Card’ summarises monitoring data collected by the DEP and our partners, as well as other relevant information collected during 2017 and early 2018, including:

  • weekly recreational water quality testing during summer months
  • monthly whole-of-estuary and catchment water quality monitoring
  • surveys of heavy metal levels in fish and shellfish
  • biological surveys (seagrass, spotted handfish, little penguins)
  • weed surveys and control actions (rice grass, karamu)

More detailed information is published in five-yearly State of the Derwent Estuary reports, available on our website.

View of Hobart city from kunanyi / Mount Wellington.

Image: Tourism Tasmania / Rob Burnett

Derwent estuary catchment zones

From the river to the sea the River Derwent and estuary supports a variety of habitats, species and human uses which are depicted in the following five illustrations. Environmental inputs that affect these areas are also highlighted.

Pollution sources, loads and trends

Pollutants of particular concern in the Derwent estuary include:

  • heavy metals, as these may be toxic to aquatic plants and animals, and accumulate in seafood — a potential health risk for local anglers.
  • excessive nutrients, as these can trigger algal blooms that reduce water clarity, smother fish habitat and deplete oxygen. Low oxygen may result in fish kills, rotten egg odours and release of nutrients and heavy metals from sediments.
  • pathogens from human sewage that are a human health risk
  • sediments, as these reduce light available to aquatic plants
  • litter — particularly floating plastics

Pollution sources

Pollution enters the Derwent estuary from many sources, commonly referred to as ‘point sources’ and ‘diffuse sources’.

Point sources include sewage treatment plants and large industries, such as the Norske Skog paper mill at Boyer and Nyrstar Hobart zinc smelter at Lutana.

Diffuse sources include stormwater runoff from urban areas as well as the larger catchment inputs carried by the Derwent and Jordan rivers. Other diffuse pollutant sources include air pollution, landfills, aquaculture operations, and wastes associated with ports and marinas. Sediments within the estuary itself may also release pollutants into the overlying waters under certain conditions.

Industry

Industries have historically been the main source of heavy metal pollution to the Derwent, however loads have declined significantly in recent years.

Contaminated groundwater at Nyrstar is now the largest remaining source, and is being captured and treated using a series of innovative projects. In 2017, over 80 tonnes of zinc and other metals were captured, together with nearly all stormwater run-off. The decreased metal load extracted in 2017 compared to 2016 is most likely due to particularly high flow volume processed in 2016.

Groundwater metals recovery (tonnes/year)
160 140 120 100 80 60 40 20 0 tonnes / year 2012/13 2013/14 2015 2016 2017 Zinc 102.8 Cadmium 2.5 Zinc 106.8 Cadmium 1.7 Zinc 89.8 Cadmium 1.9 Zinc 148.9 Cadmium 3.0 Zinc 84.6 Cadmium 2.5 Cadmium Zinc
Year Zinc Cadmium
2012/13 102.8 2.5
2013/14 106.8 1.7
2015 89.8 1.9
2016 148.9 3
2017 84.6 2.5

Sewage

Sewage treatment plants are the largest source of bioavailable nutrients, followed by the catchment, stormwater and the Norske Skog paper mill.

Effluent reuse turns a waste product into valuable, nutrient-enriched irrigation water, removing nutrients that would otherwise enter the Derwent estuary. In 2017, the volume of sewage effluent reused was similar to the previous year and accounts for approximately 20% of the regional sewage generated.

Sewage effluent re-use (tonnes/year)
4000 3500 3000 2500 2000 1500 1000 500 0 tonnes / year 2013 2014 2015 2016 2017 Bridgewater 359.5 Cameron Bay 65.5 Macquarie Point 117.3 Rokeby 500.3 Rosny 1702.3 Selfs Point 17.4 Bridgewater 440 Cameron Bay 39.2 Macquarie Point 83.6 Rokeby 543.9 Rosny 892.2 Selfs Point 47.0 Bridgewater 540.2 Cameron Bay 50.0 Macquarie Point 64.6 Rokeby 543.5 Rosny 1595.5 Selfs Point 91.0 Bridgewater 444.3 Cameron Bay 23.7 Rokeby 634.0 Rosny 1278.7 Selfs Point 95.4 Bridgewater 632.6 Cameron Bay 78.1 Rokeby 609.0 Rosny 1021.2 Selfs Point Rosny Rokeby Macquarie Point Cameron Bay Bridgewater
Year Bridge­water Came­ron Bay Macq­uarie Point Rokeby Rosny Selfs Point
2013 359.5 65.6 117.3 500.3 1702.3 17.4
2014 440.1 39.2 83.6 543.9 892.2 47.0
2015 540.2 50.0 64.6 543.5 1595.5 91.0
2016 444.3 23.7   634.0 1278.7 95.4
2017 632.7 78.1   609.0 1021.2  

Pathogens

Pathogens — usually measured indirectly using faecal indicator bacteria — can be derived from overflows or leaks from the sewerage network, as well as animal faeces associated with stormwater and rural run-off. Urban stormwater accounts for the majority of sediment and litter that enter the Derwent, with unmanaged erosion from construction sites a particular concern.

Catchment and Channel

Due to a series of taste and odour issues in drinking water, together with fish kills, and excessive algae growth in the upper estuary, a two-year collaborative catchment monitoring program was initiated by the DEP in cooperation with TasWater, Hydro Tasmania and NRM South. Results are summarised below. In the Channel, the D’Entrecasteaux and Huon Collaboration (supported by the DEP) coordinated a number of marine clean up events and will release their next Report Card summarising monitoring data later in 2018.

River Derwent water quality results

In 2015 a monitoring program was initiated by the DEP, with support from Hydro Tasmania, NRM South and TasWater to monitor nutrients, sediments and other water quality indicators in the fresh water portion of the River Derwent above New Norfolk. Water samples were collected monthly at 14 sites, including at a number of sites last monitored in 1998.

The sites include locations along the River Derwent, between New Norfolk and Wayatinah, as well as at the end of major tributaries, such as the Plenty, Styx, Tyenna, Clyde, Broad, Dee, Ouse and Florentine Rivers. The water quality of the River Derwent in 1998 was excellent however an observed increase in nutrients in the Derwent estuary near New Norfolk, plus the findings of the 2011 River Derwent catchment review, prompted the DEP and other organisations to revisit the monitoring program.

The monitoring revealed that nutrients are predominately derived from aquaculture during summer and from agricultural sources in winter. Water quality across the catchment varied considerably over the two-year sampling period, with lowest nutrient concentrations observed in the upper catchment (below Wayatinah) and Broad River, both of which receive run-off from largely natural, forested catchments.

Elevated dissolved nitrogen and phosphorus levels were observed in both agriculture dominated catchments (e.g. the Ouse, Clyde) and those receiving effluent from large fish hatcheries (e.g. Florentine and Tyenna). Based on the report recommendations, our next steps will involve working with our stakeholders, including representatives of aquaculture and agriculture, to identify immediate actions to reduce nutrients in the river. Read the full report.

Estimated combined loads

Nutrients: dissolved inorganic nitrogen (tonnes/year)
800 700 600 500 400 300 200 100 0 tonnes / year 2013 2014 2015 2016 2017 River 201 Stormwater 49 Sewage 398 Industry 43 River 82 Stormwater 49 Sewage 419 Industry 30 River 116 Stormwater 49 Sewage 428 Industry 35 River 245 Stormwater 49 Sewage 342 Industry 32.5 River 86 Stormwater 49 Sewage 349 Industry 32 Industry Sewage Stormwater River
Year River Storm­water Sewage Indu­stry
2013 201 49 398 43
2014 82 49 419 30
2015 116 49 428 35
2016 245 49 342 32.5
2017 86 49 349 32
Nutrients: total phosphorus (tonnes/year)
250 200 150 100 50 0 tonnes / year 2013 2014 2015 2016 2017 River 63 Stormwater 30 Sewage 88 Industry 8 River 19 Stormwater 30 Sewage 87.7 Industry 20.2 River 21 Stormwater 30 Sewage 86 Industry 13 River 43 Stormwater 30 Sewage 99 Industry 10.5 River 14.9 Stormwater 30 Sewage 80.9 Industry 12.6 Industry Sewage Stormwater River
Year River Storm­water Sewage Indu­stry
2013 63 30 88 8
2014 19 30 87.7 20.2
2015 21 30 86 13
2016 43 30 99 10.5
2017 14.9 30 80.9 12.6
Zinc (tonnes/year)
160 140 120 100 80 60 40 20 0 tonnes / year 2013 2014 2015 2016 2017 Nyrstar groundwater 120 Nyrstar outfall 2.7 Stormwater 7 Sewage 1.2 Nyrstar groundwater 120 Nyrstar outfall 2.7 Stormwater 7 Sewage 1.2 Nyrstar groundwater 120 Nyrstar outfall 1 Stormwater 7 Sewage 1.2 Nyrstar groundwater 120 Nyrstar outfall 6.5 Stormwater 7 Sewage 1.2 Nyrstar groundwater 120 Nyrstar outfall 0.9 Stormwater 7 Sewage 1.2 Sewage Stormwater Nyrstar outfall Nyrstar groundwater
Year Nyr­star ground­water Nyr­star out­fall Storm­water Sewage
2013 120 2.7 7 1.2
2014 120 2.7 7 1.2
2015 120 1.0 7 1.2
2016 120 6.5 7 1.2
2017 120 0.9 7 1.2
Sediments as total suspended solids (tonnes/year)
40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 tonnes / year 2013 2014 2015 2016 2017 River 22,260 Stormwater 7,996 Sewage 285 Industry 172 River 9,618 Stormwater 7,996 Sewage 217.4 Industry 296 River 12,799 Stormwater 7,996 Sewage 309.3 Industry 414.6 River 26,662 Stormwater 7,996 Sewage 324 Industry 935.6 River 7,034 Stormwater 7,996 Sewage 195.6 Industry Sewage Stormwater River
Year River Storm­water Sewage Indu­stry
2013 22260 7996 285 172
2014 9618 7996 217.4 296
2015 12799 7996 309.3 414.6
2016 26662 7996 324.0 935.6
2017 7034 7996 195.6 809.8
Organic matter as biochemical oxygen demand (tonnes/year)
1600 1400 1200 1000 800 600 400 200 0 tonnes / year 2013 2014 2015 2016 2017 Sewage 396 Norske Skog Boyer 108 Sewage 367.4 Norske Skog Boyer 172 Sewage 404.4 Norske Skog Boyer 311 Sewage 590.9 Norske Skog Boyer 852.6 Sewage 466.4 Norske Skog Boyer 356 Norske Skog Boyer Sewage
Year Sewage Norske Skog Boyer
2013 396 108
2014 367.4 172
2015 404.4 311
2016 590.9 852.6
2017 466.4 356

Did you know?

Effluent reuse increased markedly from the Bridgewater plant in 2017 compared to previous years which has reduced effluent and associated nutrients to the upper estuary (TasWater).

The Derwent Estuary Program is a partnership between state and local government and industry to make the Derwent a world class asset by sharing science for the benefit of nature, the economy and the community.

Environmental problem: plastic bags.

Image: iStock / richcarey

Derwent water and sediment quality

The DEP ambient and recreational water quality monitoring programs have been operating for 19 years and provide a basis for assessments relating to swimming at beaches, and a whole of estuary health check. Current emphasis includes keeping tabs on dissolved oxygen levels and nutrients in the upper estuary.

Climatic conditions

Rainfall, as measured at the Ellerslie Road (BOM) weather station in Hobart, recorded a slightly wetter than average year. This result is due to more than half the summer rain falling over a three-day period in early December (92 mm), with the wettest December recorded in 23 years. If not for this single event it would have been a significantly drier than average summer. River Derwent flow during summer 2016–17 was the second lowest it had been in 22 years. Flow volume was markedly higher in the summer of 2017–18.

Rainfall in Hobart, Bureau of Meteorology
125 100 75 50 25 0 rainfall (mm) month (2017) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan 2017 60mm Jan 133 year average 47.5mm Feb 2017 10.4mm Feb 133 year average 39.5mm Mar 2017 37mm Mar 133 year average 44.7mm Apr 2017 21.6mm Apr 133 year average 50.3mm May 2017 28.4mm May 133 year average 46.7mm Jun 2017 6.6mm Jun 133 year average 53.9mm Jul 2017 37.2mm Jul 133 year average 52.4mm Aug 2017 65mm Aug 133 year average 53.5mm Sep 2017 46.2mm Sep 133 year average 53.2mm Oct 2017 33.4mm Oct 133 year average 61.3mm Nov 2017 46.4mm Nov 133 year average 54.2mm Dec 2017 101mm Dec 133 year average 56.5mm 2017 rainfall 133 year average
Month 2017 rainfall (mm) 133 year average (mm)
January 60 47.5
February 10.4 39.5
March 37 44.7
April 21.6 50.3
May 28.4 46.7
June 6.6 53.9
July 37.2 52.4
August 65 53.5
September 46.2 53.2
October 33.4 61.3
November 46.4 54.2
December 101 56.5
Cracking clay with samphire (Sarcocornia sp.).
Cracking clay with samphire (Sarcocornia sp.).

Image: Derwent Estuary Program

Sandy Bay glimpsed through a break in the clouds from kunanyi / Mount Wellington. Image: Steve Lacy
Sandy Bay glimpsed through a break in the clouds from kunanyi / Mount Wellington.

Image: Steve Lacy

Beach walk, Howrah, Tasmania.
Beach walk, Howrah, Tasmania.

Image: Kieran Bradley

Swimming in the Derwent

Each summer recreational water quality is monitored at about 35 beaches and bays around the estuary through a collaborative State and Local Government program. Sampling is conducted weekly from December through March at the locations shown in our sampling and discharge points map.

To describe the risk level to swimmers a colour coded system is used based on five years of monitoring data: green indicates good, yellow indicates fair, and red indicates poor water quality.

Thirteen of the Derwent’s eighteen swimming sites are currently classified as having good water quality, four are fair and two are poor. The best water quality sites are at Hinsby, New Norfolk, Little Sandy Bay and Little Howrah. The western end of Nutgrove Beach received a poor rating but extensive pipe work by Hobart City Council and TasWater has seen water quality improve here (see recent management actions for details). Blackmans Bay South was downgraded to a poor rating last season. Extensive efforts to identify the source of contamination are being undertaken by Kingborough council and TasWater. Of the 21 bays, coves and other sites monitored, nine are ranked as good, four less than the previous season. The number of bays with fair water quality increased from three to six, whilst the number of poor bay sites increased from five to six (the mouth of Hobart Rivulet and Browns River, Cornelian Bay and Marieville Esplanade).

Water quality improved at several beach sites in 2017–18 but there was a decline in water quality at some bays. High rainfall accounts for some of the poor results, but not all. It is recommended that sanitary investigations continue to identify and correct sources of faecal contamination. Most urban areas experience poor water quality after heavy rain. Swimming is not recommended in the Derwent for several days after heavy rain and never in the vicinity of stormwater drains or urban rivulets.

Little Sandy Bay Beach.
Little Sandy Bay Beach.

Image: Derwent Estuary Program

Taking a water sample from the beach.
Taking a water sample from the beach.

Image: H. Bobbi, DHHS

Water quality indicators

The DEP coordinates a whole-of-estuary monitoring program that integrates sampling carried out by the DEP and EPA Division, Nyrstar Hobart, Norske Skog and TasWater. Water quality is monitored each month at 27 sites for indicators such as temperature, salinity, dissolved oxygen, suspended solids, nutrients, organic carbon, chlorophyll a and heavy metals. This information is used to document conditions and trends over time and to provide data for estuarine modelling and process studies.

Dissolved oxygen levels in the Derwent are generally high except periodically in the area between Bridgewater and New Norfolk. During summer months when water temperatures are high and river flows are low, the deeper channels in this area tend to be oxygen poor, with adverse impacts on bottom-dwelling organisms and some species of fish. Low oxygen levels can also result in the release of nutrients and heavy metals from underlying sediments. Dissolved oxygen was again very low in bottom waters of the upper Derwent estuary in summer/ autumn 2016–17 and 2017–18, but hypoxia (oxygen deficiency) was not as severe at New Norfolk in 2017–18 compared to 2016–17.

2017 dissolved oxygen levels at New Norfolk (at depth)
100 90 80 70 60 50 40 30 20 10 0 dissolved oxygen (% saturation) month (2017) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 17 Jan 2017 11.8% 21 Feb 2017 33% 21 Mar 2017 20.4% 11 Apr 2017 22.1% 16 May 2017 32% 20 Jun 2017 42.3% 18 Jul 2017 54.5% 15 Aug 2017 96.3% Sep 2017 98.2% (interpolated) 17 Oct 2017 100% 21 Nov 2017 38.3% 19 Dec 2017 93.6%
Month Dissolved oxygen (% saturation)
January 11.8
February 33
March 20.4
April 22.1
May 32
June 42.3
July 54.5
August 96.3
September 98.2
October 100
November 38.3
December 93.6

Seagrass health update

The extensive meadows of aquatic plants in the upper Derwent estuary are showing signs of stress due to human population pressures. Their decline is a problem as seagrass assists with nutrient removal, sediment stabilisation, as well as providing food and habitat for birds, fish and crabs.

The principal factors restricting the health of this habitat are light, temperature, nutrients and salinity. Although all plants require some amount of nutrients, algae is quicker to respond to elevated nutrients than the longer-lived and slower growing seagrass, and can grow so densely that the underlying seagrass cannot get enough light to survive or reproduce.

Between spring 2015 and autumn 2017, seagrass condition severely declined and in areas known to support seagrass, it covered just 10% of that area, with the remaining 90% consisting of either bare substrate, or a dense smothering of green algae. However, in the spring/summer of 2017–18, seagrass recovered without the expected increase in algal smothering. By early autumn 2018, approximately 60% of this area had returned to seagrass. In Herdsman’s Cove at the mouth of the Jordan River, seagrass cover increased to 37%, up from 2%. The observed improvement provides an excellent opportunity to identify potentially related environmental changes.

Contaminated sediments

Levels of heavy metals in Derwent estuary sediments are among the highest in Australia. Derwent sediments tend to be fine-grained and organic-rich and significantly exceed national sediment quality guidelines for zinc, copper, mercury, lead, cadmium and arsenic.

The most recent survey (2012) confirmed that metal levels are highest in the mid estuary and at depth, with some slight improvements observed in a few areas.

Australian fairy penguins.

Image: iStock / jswax

Habitats and species

Important habitats of the Derwent include rocky reefs, saltmarshes and wetlands. The Derwent is also home to huge numbers of plants and animals. Two of note are the spotted handfish and the little penguin and their conservation is supported by the DEP in cooperation with local councils, scientists, State Government and the community. Human health is a key reporting priority for the DEP, particularly heavy metal levels in fish and shellfish.

Estuarine habitat and species

Spotted handfish.
Spotted handfish.

Image: Rick Stuart-Smith

Surveys of the Derwent estuary indicate that unvegetated, soft-bottom habitats are by far the most abundant habitats in the estuary (86%), followed by seagrass and macrophytes (7%; primarily in the upper estuary), tidal sandflats (6%; primarily in Ralphs Bay) and rocky reefs (1%; primarily in the lower estuary). Detailed surveys by the CSIRO of nine Derwent estuary spotted handfish colonies were carried out again in 2017 using a new survey method. The number of handfish have declined and no handfish were observed in Ralphs Bay. Numbers of juvenile fish at all sites are critically low. A captive breeding program has been initiated and this is a promising step with fish breeding at Seahorse World in Tasmania, the CSIRO and at the Melbourne aquarium. In the Derwent, artificial spawning substrates (made of ceramic) have been planted out at key sites to improve breeding success. The use of eco-moorings for boats better protects the seafloor and a small number have been installed at boat and yacht clubs in Sandy Bay which will help improve spotted handfish habitat.

In 2018 the Handfish Conservation Project was established where all donations received will be used to support research to prevent these critically endangered fish becoming extinct.

Black swan.
Black swan.

Image: Dick Daniels

Heavy metals in seafood

Oysters and mussels from the Derwent contain high levels of heavy metals, particularly zinc, lead and cadmium. While levels appear to have declined since 2003 in some areas (i.e. above the Tasman Bridge), they are still far in excess of national food standards. Mercury levels exceed national food standards in several species of Derwent caught fish — particularly black bream — and to a lesser degree flathead and trout.

Limited sampling suggests that levels are lower in other recreationally-targeted fish (e.g. whiting, Australian salmon, mullet, cod and flounder). Based on the most recent (2017) monitoring results for flathead, oysters and mussels, there has been no change in current health advice, which is as follows:

  • Don’t eat shellfish collected from the Derwent (including Ralphs Bay)
  • Don’t eat any bream from the Derwent (including Browns River)
  • Limit consumption of other Derwent-caught fish to no more than 2 meals/week, or 1 meal/week for pregnant and breastfeeding women, women planning to become pregnant and young children

The seafood safety survey to assess recreationally targeted fish (other than flathead) will be repeated in 2019.

Marine pests, weeds and disease

The Derwent estuary is extensively colonised by introduced marine species. At least 79 invasive species have been recorded, including four species of particular national concern: northern Pacific seastar, European green crab, Japanese seaweed, and European clam. A number of other species (e.g. New Zealand half crab, New Zealand seastar, and New Zealand screw shell) also pose a significant threat to the ecology of the estuary.

Rice grass — an invasive intertidal weed — has been successfully managed in the Derwent through annual surveys and control actions, and the area of infestation had been reduced from two hectares in 1995 to zero in 2009 and 2010. Surveys in 2015 found several small patches in the middle estuary region. These sites continue to be monitored and in 2017 and 2018 no rice grass was observed. A Derwent region weeds group has been established by the DEP with the aim of identifying emerging weed threats, sharing knowledge and resources. The rice grass survey also provides the opportunity to survey and inform land managers of other weeds infesting the mid-estuary.

Surveying the mid-estuary foreshore for rice grass and other weeds.
Surveying the mid-estuary foreshore for rice grass and other weeds.

Image: Derwent Estuary Program

Karamu.
Karamu.

Image: Jon Sullivan

Karamu (Coprosma robusta) is an evergreen shrub originating from New Zealand that is a declared weed under the Tasmanian Weed Management Act 1999, requiring landholders to remove it from their property. The upper Derwent estuary had previously been identified as the largest infestation in Tasmania. While much has been eradicated over the past five years, a large dense infestation remains around New Norfolk. A winter boat survey confirmed the upper location of Karamu on the main trunk of the Derwent, starting at the riffles above Bryn Estyn. Primary control works were conducted by the Derwent Catchment Project on private land in and around New Norfolk following the survey. To guide the management of Karamu over the next 7 years a comprehensive management plan was developed by the stakeholders. Active and ongoing management of Karamu involves the Derwent Catchment Project, Department of State Growth, Parks and Wildlife Service, NRM South, DEP, Crown Land Services, and the Derwent Valley Council.

Did you know?

We are starting to see a decline in heavy metal levels in the water as well as in shellfish thanks to the interception of contaminated groundwater at Nyrstar.

Sampling sites and discharge points

The DEP Beach Watch and ambient water quality monitoring sites are located on the map along the location of waste water treatment plants and our industry partners Nyrstar and Norske Skog Boyer.

Derwent estuary map kunanyi / Mount Wellington HOBART New Norfolk Bridgewater Austins Ferry Old Beach Claremont Glenorchy Moonah New Town Lindisfarne Bellerive Howrah Tranmere Rokeby Lauderdale South Arm Sandy Bay Taroona Kingston Blackmans Bay Tinderbox Bridgewater Causeway Bowen Bridge Tasman Bridge Iron Pot North West Bay Ralphs Bay Ambient monitoring site (temperature, salinity, pH, dissolved oxygen, nutrients, chlorophyll a, metals) New Norfolk (Fitzgerald Park) Windermere Bay Beach Nutgrove Beach (east) Nutgrove Beach (west) Little Sandy Bay (south) Little Sandy Bay (north) Hinsby Beach Taroona Beach Kingston Beach (north) Kingston Beach (mid) Kingston Beach (south) Blackmans Bay (mid) Blackmans Bay (south) Bellerive Beach Howrah Beach (east) Howrah Beach (mid) Howrah Beach (west) Little Howrah Beach Cornelian Bay Beach Cameron Bay Old Beach Jetty Elwick Bay Yacht Club New Town Bay Prince of Wales Bay Geilston Bay Lindisfarne Bay Montagu Bay Mid-River Swim Hobart Rivulet (mouth) Regatta Pavilion Victoria Dock Waterman’s Dock Brooke Street Pier Sullivans Cove Marieville Esplanade Kangaroo Bay Brown’s River MONA jetty Berriedale Bay, at MONA Brighton Brighton East Risdon East Risdon New Norfolk New Norfolk Bridgewater Bridgewater Cameron Bay Cameron Bay Rosny Rosny Rokeby Rokeby Blackmans Bay Blackmans Bay Prince of Wales Bay Prince of Wales Bay Macquarie Point Macquarie Point Sandy Bay (outfall from Selfs Point) Sandy Bay (outfall from Selfs Point) Selfs Point (outfall at Sandy Bay) Selfs Point (outfall at Sandy Bay) Norske Skog Paper Norske Skog Paper Nyrstar Hobart Smelter Nyrstar Hobart Smelter Water quality monitoring sites in 2017 Beach and bay monitoring sites (enterococci) Good water quality Fair water quality Poor water quality Ambient monitoring sites (temperature, salinity, pH, dissolved oxygen, nutrients, chlorophyll a, metals) Sewage treatment plant discharges in 2017 < 1000 kL/d 1000–5000 kL/d > 5000 kL/d Industrial discharges in 2017 > 50,000 kL/d EXPLORE MAP EXPLORE MAP

Use the “Explore map” button to find the Beach Watch and ambient water quality monitoring sites, the location and discharge rates of waste water treatment plants and large industry. The layers on the map can be viewed separately or together. Or view a list of the locations in the tables that follow.

Beach Watch water quality monitoring sites in 2017
Location Result
New Norfolk (Fitzgerald Park) Good
Windermere Bay Beach Fair
Nutgrove Beach (east) Fair
Nutgrove Beach (west) Poor
Little Sandy Bay (south) Good
Little Sandy Bay (north) Good
Hinsby Beach Good
Taroona Beach Good
Kingston Beach (north) Fair
Kingston Beach (mid) Good
Kingston Beach (south) Fair
Blackmans Bay (mid) Good
Blackmans Bay (south) Poor
Bellerive Beach Good
Howrah Beach (east) Good
Howrah Beach (mid) Good
Howrah Beach (west) Good
Little Howrah Beach Good
Cornelian Bay Beach Poor
Bay Watch water quality monitoring sites in 2017
Location Result
Cameron Bay Poor
Old Beach Jetty Good
Elwick Bay Yacht Club Fair
New Town Bay Fair
Prince of Wales Bay Good
Geilston Bay Fair
Lindisfarne Bay Good
Montagu Bay Good
Mid-River Swim Good
Hobart Rivulet (mouth) Poor
Regatta Pavilion Fair
Victoria Dock Good
Waterman’s Dock Poor
Brooke Street Pier Good
Sullivans Cove Good
Marieville Esplanade Poor
Kangaroo Bay Good
Brown’s River Poor
MONA jetty Good
Berriedale Bay, at MONA Fair
Sewage treatment plant discharges in 2017
Location Result
Brighton < 1000 kL/d
East Risdon < 1000 kL/d
New Norfolk 1000–5000 kL/d
Bridgewater 1000–5000 kL/d
Cameron Bay 1000–5000 kL/d
Rosny 1000–5000 kL/d
Rokeby 1000–5000 kL/d
Blackmans Bay 1000–5000 kL/d
Prince of Wales Bay > 5000 kL/d
Macquarie Point > 5000 kL/d
Sandy Bay (outfall from Selfs Point) > 5000 kL/d
Industrial discharges in 2017
Location Result
Norske Skog Paper > 50,000 kL/d
Nyrstar Hobart Smelter > 50,000 kL/d

Recent management actions

The Derwent Estuary Program provides science to guide management. Here are several management examples highlighting how pollution has and is being, reduced in the Derwent estuary and catchment.

Nutrient reduction from the Meadowbank Hatchery

The Huon Aquaculture Meadowbank Facility. Image: Huon Aquaculture
Huon Aquaculture Meadowbank Facility

Image: Huon Aquaculture

The Huon Aquaculture Meadowbank Facility located on the River Derwent slightly downstream of the Meadowbank Dam saw continuing reductions within its nutrient levels discharging into the River Derwent from its Aquaculture operations.

Between 2014 and 2018 there was a reduction in: total nitrogen (56%), combined ammonia and ammonium (76%), and total phosphorous (68%). These reductions are directly related to the immediate removal of solid waste from the flow utilising microstraining filters and the continued establishment of the onsite settlement dam and wetland. Flow meters measuring water inputs into the site were integrated with the site’s data system to allow for accurate development of mass loadings for these nutrients. This will allow site managers to better assess its actual impact and aim for continuous improvement of its discharging water quality moving forward.

Finding and fixing the source stormwater pollution at Nutgrove Beach (west)

Current sign warning of poor water quality at Nutgrove beach (west) may soon be a thing of the past. Image: Olivia Skeers.
Current sign warning of poor water quality at Nutgrove beach (west) may soon be a thing of the past.

Image: Olivia Skeers

Last summer, a coordinated effort by City of Hobart, TasWater and DEP identified a cracked pipe and two cross-connections from sewer to stormwater reaching Nutgrove beach (west).

In the spring/summer of 2017–18, TasWater undertook significant repairs and sewer-pipe realignment and City of Hobart removed the direct cross-connections. Sampling throughout the 2017–18 season has shown that this coordinated effort has resulted in a marked improvement in the rolling 5-year results for enterococci levels (a faecal indicator bacteria) at Nutgrove Beach west, despite it remaining in the ‘poor’ category. It is hoped that results in the coming season continue to show reduced enterococci levels so the ‘no-swimming’ recommendation can be removed.

Prince of Wales Bay clean up

Before the clean up at Prince of Wales Bay. Credit: Derwent Estuary Program.
Before the clean up at Prince of Wales Bay.

Image: Derwent Estuary Program

After the clean up at Prince of Wales Bay. Credit: Derwent Estuary Program.
After the clean up at Prince of Wales Bay.

Image: Derwent Estuary Program

In 2018, the DEP coordinated two clean up events at Prince of Wales Bay. The first was a Business Clean Up Australia Day event which included a team of over 20 volunteers from DEP partners including Tas Water, Nyrstar and Glenorchy City Council. The team collected 80 bags of rubbish in three hours including larger items such as metal drums, boxes, building materials, pipes, crates, polystyrene and rope.

To finish the job the DEP coordinated a second clean up event, this time with volunteers from seven local business in Prince of Wales Bay. With improved access via the use of a boat on loan from the Plastic Fabrications Group, the team disposed of approximately 800kg of rubbish in four hours leaving the shoreline relatively clean. The two events were a success and encouraged networking across local businesses and council and raised awareness of a large-scale community issue.

Annual Beach Watch inter-calibration exercise

Environmental Health Officers from six councils at the inter-calibration. Image: H. Bobbi, DHHS.

Image: H. Bobbi, DHHS

Each year, in preparation for the summer beach water quality monitoring (Beach Watch), the DEP facilitates a training session for environmental health officers from our six council partners and members of the Department of Health and Human Services.

The session is held at one of our lovely local beaches to ensure that everybody is familiar with the required sampling techniques and handling requirements to guarantee consistency of results. Topics include common pitfalls to avoid contamination of the sample, how best to keep it cold until delivered to the Public Health Laboratory in New Town, how to fill in lab submission forms with climate data and general observations, and how to stay safe while sampling. Everybody brings their waders and sample rods, and sampling methods are reviewed and practiced together, followed by a comparison of results to confirm uniformity. It is also an opportune time to get together at the start of the summer swimming season for general support, and for ‘old hands’ to share their knowledge and experience with newcomers.

Derwent little penguin update

Little Penguin (Eudyptula minor) family exiting burrow.

Image: JJ Harrison

Little penguin monitoring has been given a boost with assistance from DPIPWE’s Land Tasmania, who have produced an Arc-GIS Collector App. The App enables efficient collection and reporting of little penguin data and instant access to the data by land managers.

Monitors are already using the App in the field and the consolidation of recent and historical monitoring data has occurred, with the invaluable help of an IMAS Honours student. This year also saw weeds controlled at a difficult to access little penguin site on the western shore of the Derwent, along with the addition of some new nest boxes thanks to the support of Kingborough Council. At the largest little penguin colony on the Derwent, volunteers from the Friends School undertook rubbish runs, marked all un-marked nest boxes, weeded and planted native vegetation which has helped improve the site.

Reeds

Image: iStock / narcisa