Blackwater event in Wannon River

The Glenelg Hopkins Catchment Management Authority is aware of a fish death event in the Wannon River.

Blackwater and low dissolved oxygen levels in the waterways are causing stress or death of native fish in several locations.

These events are usually associated with large rain events and water sitting on the floodplains for extended periods.

Glenelg Hopkins CMA Executive Manager Waterways, Chris Solum, said the event was challenging but not unexpected considering recent flooding and weather conditions.

MEDIA RELEASE: Blackwater event in Wannon River

What is blackwater?

What is toxic blackwater?

Put simply, toxic blackwater is a term used when high levels of organic material and tannins in a river discolour the water making it appear black – like a really-strong pot of tea. It occurs when large amounts of organic material on floodplains are covered with water in warm conditions and large amounts of dissolved carbon get into the water.

Bacteria multiply quickly to use the massive amounts of dissolved carbon (it’s a feeding frenzy), but in doing so the bacteria multiply and use up a lot of the oxygen in the water – oxygen that fish need. This is also called a hypoxic blackwater event.