Water quality

The Sandy Bay rivulet meets the Derwent

Good water quality is essential for the health of the Derwent estuary's habitat and species; as well as for the people who live around its shores..

Water quality can be impacted by:

  • 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 in the Derwent is relatively good, compared to many other estuaries around Australia. Levels of suspended solids tend to be low, except after major flood events. During winter months, the estuary is coloured by naturally dark, tannin-rich river water from the upper catchment.

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 mid-estuary sites, in bays and at depth, reflecting inputs from sewage treatment plants and sediment. Nuisance algal blooms are rare.

The Derwent Estuary Program runs a number of initiatives aimed at monitoring and improving water quality including Monitoring and Science, Heavy Metals, Stormwater and Water Sensitive Urban Design projects.

Juvenile Spotted Handfish (Brachionichyths hirsutus)

Restoring and promoting the Derwent estuary