River Murray water users may notice a darker water colour and dead or distressed fish in parts of the River Murray as a natural phenomenon, known as Blackwater, moves through South Australia’s River Murray system.
Blackwater occurs when organic material, such as leaves and wood from the forest floor and floodplain, are washed into waterways. As its name suggests, blackwater creates a black appearance in the water and a strong smell.
As the organic matter decays, it results in low water oxygen levels which may cause fish to die.
PIRSA has already received several reports of fish kills in the upper reaches of the River Murray and it is expected that more reports will be made as the blackwater moves downstream.
Members of the public are urged to report large numbers of dead fish or other aquatic animals seen during the blackwater event to the 24-hour Fishwatch hotline on 1800 065 522.
For further information visit www.pir.sa.gov.au/biosecurity/aquatics/mass_fish_die-off
Quotes attributable to PIRSA Fisheries and Aquaculture Director Policy Sean Sloan
Blackwater is a natural phenomenon and while it may look and smell unpleasant, it is non-toxic and poses no direct public health risk.
Blackwater does not increase the risk of infection or illness when swimming or undertaking other recreational activities on the River Murray, however, people should take additional care where visibility is decreased as there is a higher risk of physical injury from submerged objects.
River users and visitors to the area can still enjoy recreational fishing and boating along the River Murray, especially as the holiday season approaches, however any dead or dying fish should not be taken for consumption.
While some people may be concerned about blackwater, particularly when seeing deceased or distressed fish, it is important to remember that this natural event does contribute to major improvements in the long term health of the River Murray.
Livestock owners along the Murray are encouraged to top up tanks while the water is still fresh and to not pump until the blackwater passes. While blackwater is acceptable for animals to drink, they will naturally prefer cleaner water.
A fish kill is a sudden mass mortality of fish or marine organisms, which can be caused by a range of factors, including water quality changes, pollution or infection, however most fish kills are the result of natural events and changes in the local environment.
The blackwater event has been generated by significant high flows onto the floodplain upstream of South Australia. PIRSA, along with the Department of Environment, Water and Natural Resources and SA Water, is working closely to monitor the blackwater as it moves through South Australia.
It is too early to predict how long this event will last as dissolved oxygen levels can change quickly as a result of flows upstream, temperature and wind effects.
For further information on blackwater visit www.environment.sa.gov.au/managing-natural-resources/river-murray/about-the-river/issues-for-river-health