A report card looking at the health of the Derwent has found that the condition of the estuary declined in several areas during 2011-12.
The 2012 State of the Derwent Report Card summarises monitoring data collected by the Derwent Estuary Program (DEP) and partners in the area between New Norfolk and the Iron Pot Light.
Releasing the 2012 report today, DEP Director Christine Coughanowr said it provides a watching brief on the State of the Derwent estuary.
"As in previous years, this includes trends in industrial, sewage and stormwater discharges, monitoring results for swimming beaches and heavy metals in seafood, as well as actions taken to clean-up the Derwent," Ms Coughanowr said.
"The report shows water quality had declined during 2011 and the early part of 2012, due in part to higher than average rainfall causing an increase in stormwater and catchment runoff."
"Most industrial inputs continued to decline, however the amount of wastewater discharged by sewage treatment plants has increased."
"The increase in treated sewage discharged to the Derwent can be explained in part by the above average rainfall, which resulted in both a higher volume of stormwater inflow as well as a reduced demand for wastewater for irrigation," Ms Coughanowr said.
Ms Coughanowr said a major study of heavy metals and nutrients has highlighted the need to manage the estuary within a broader context that also includes the River Derwent catchment and D'Entrecasteaux Channel.
"There have been some early signs of increasing nutrient levels and low dissolved oxygen in recent years, particularly in the area between new Norfolk and Bridgewater. This is something we need to keep a close eye on - particularly given the valuable wetlands and fisheries in this area," she said.
The water quality at swimming beaches and bays declined at a number of sites in 2011-12, however most beaches retained their current status. Sites with the best water quality include New Norfolk Esplanade, Little Sandy Bay Beach, Hinsby Beach, Blackmans Bay and Opossum Bay.
Windermere Beach and the western end of Nutgrove Beach again received poor water quality ratings. Ms Coughanowr said investigations have been recommended to identify and address pollution sources at these sites.
Water quality at a number of bays also declined in 2011-12 - particularly at Lindisfarne, Geilston and Kangaroo Bays - however the Hobart Waterfront improved significantly.
The report card also reports on seafood safety monitoring, with heavy metal levels in Derwent estuary oysters, mussels and black bream found to remain well above national food safety standards.
Public health advice on Derwent caught fish and shellfish:
• Do not eat bream.
• Limit consumption of flathead and other fish to twice a week.
• Some people should further limit consumption to once a week, including:
o pregnant and breastfeeding women
o women planning to become pregnant
o children aged six years and younger.
• If you eat fish from the Derwent it is best to avoid eating fish from other sources in the same week.
• Do not collect and eat wild shellfish.
"To re-enforce this message, signage will be installed in various areas around the estuary in early 2013," Ms Coughanowr said. More information can be found in the recently updated brochure 'Should I eat Shellfish and Fish from the Derwent?' at: www.derwentestuary.org.au
Key management actions and initiatives carried out by the DEP partnership in 2011-12 include:
• Further investment in groundwater management and treatment at Nyrstar, with a record 130 tonnes/year of zinc extracted from groundwater.
• Several major stormwater treatment projects are underway, including the $20 million Derwent Park stormwater harvesting project.
• Annual weed surveys and treatment continue in an effort to eradicate rice grass and prevent the spread of 'karamu' into high value wetlands.
• Population surveys and recovery actions to improve the breeding success of the Derwent's critically endangered spotted handfish.
• Development of educational materials and guided walks for local schools.
"The information contained in the annual Derwent Report Card is used by all levels of government, industries and the community to gauge the state of the estuary," Ms Coughanowr said.
"The poorer water quality reported in the 2012 Report Card should be taken in the context of higher-than-average rainfall, and may be a temporary condition. However, it is also a reminder that we need to be vigilant and proactive to ensure that the health of the estuary continues to improve in the longer term."
The Derwent Estuary Program (DEP) is a regional partnership between the Tasmanian State Government, councils, businesses, scientists and community-based groups to restore and promote the Derwent estuary.
For a full copy of the 2012 State of the Derwent Report Card, go to www.derwentestuary.org.au or pick up a copy at Council or Service Tasmania offices.