Blackwater is a natural phenomenon that can occur after a significant rainfall event, when organic matter on the floodplain (e.g. leaves and wood) is washed into the river. The breakdown of organic matter consumes dissolved oxygen, which reduces the level of dissolved oxygen in the water. The water is blackish in appearance and has a strong unpleasant smell.
Blackwater is in the South Australia’s portion of the River Murray. It is expected that the main river channel and potentially the connected backwaters from the border to the lower lakes will experience blackwater.
This blackwater is event is a result of high flows across New South Wales and Victoria washing large amounts of organic matter from the floodplain into the River Murray.
Blackwater in the River Murray poses no direct public health risk. In a small number of people blackwater may cause a skin irritation due to sensitivity to natural organic matter in the water.
Blackwater is safe to swim in and around. River users can still enjoy recreational fishing, yabbying and boating along the River Murray.
Blackwater’s low dissolved oxygen levels can cause fish and crustaceans to die or become distressed. Any dead or dying fish and crustaceans should not be eaten. Report sightings of large numbers of dead or distressed fish to the 24-hour Fishwatch hotline on 1800 065 522.
DEW, SA Water, Murray-Darling Basin Authority and other government agencies are working closely to monitor the situation.
Blackwater is reported by low dissolved oxygen levels generally below 3 mg/L.
The duration of a blackwater event differs with each event as dissolved oxygen levels can change quickly due to flows upstream, temperature and wind effects. For context the previous blackwater events in 2011 and 2012 lasted several months.
Impacts on fish and crustaceans
Large fish can become distressed when dissolved oxygen levels fall below 2.0 mg/l.
PIRSA have received a number of fish kill reports thought to be caused by the blackwater event in the upper River Murray region of South Australia. PIRSA will continue to monitor as the blackwater event moves downstream.
Further information about fish kills and how to report is available on the PIRSA website.
Water supplies and quality
It is recommended not to drink water from the River Murray at any time unless it is treated.
The water quality challenges presented by blackwater can be effectively treated via SA Water’s treatment processes and therefore do not currently pose a drinking water quality issue.
Further information about blackwater water quality is available on the SA Water website.
Blackwater water is acceptable for livestock and animals to drink, but they prefer cleaner water.
Read more about:
- Use our project map to find out about projects happening at specific sites along the river
- Riverbank collapse, inundation, infrastructure and other data and maps on EnviroData