Water quality

Water quality can be impacted by a number of factors, including:

• Temperature, salinity and pH
• Dissolved oxygen
• Clarity, colour and suspended particulate matter
• Nutrients and organic matter
• Phytoplankton, chorophyll a and nuisance plant growth
• Pathogens and faecal bacteria
• Heavy metals

Water clarity is generally good in the Derwent, and suspended particulate levels are low, except after heavy rain. Faecal bacterial levels are also typically low at most sites, with the majority of beaches and bays receiving a good rating.

Nutrient levels vary seasonally, with the highest values measured in winter months when nutrient-rich, sub-Antarctic waters extend north to southeastern Tasmania. Nutrient levels are generally highest at upper and mid-estuary sites, reflecting inputs from sewage treatment plants, industry and the catchment. Until recently, nuisance algal blooms were rare, however recent algal blooms in the upper estuary, together with seagrass loss and taste and odour issues in the Hobart water supply, are indicative of increasing nutrient loads to the river and estuary.

The Derwent Estuary Program coordinates a number of initiatives to monitor and improve water quality including recreational and ambient water quality monitoring programs, dissolved oxygen and seagrass surveys, sediment and seafood surveys, heavy metal and nutrient investigations,as well as stormwater and Water Sensitive Urban Design projects.