Blackwater event kills thousands of juvenile fish and prawns

17 February 2020

Rotting vegetation takes oxygen out of water

A blackwater event has killed thousands of juvenile fish and prawns in the Cudgera Creek Estuary at Hastings Point.

Council has confirmed that the cause of the fish kill is a total absence of dissolved oxygen within the waters of the creek.

“This is called a blackwater event,” Waterways Program Leader Tom Alletson said.

“The floodplain of Cudgera Creek, like that of Cudgen (Kingscliff) and Mooball (Pottsville) creeks, has been inundated by stagnant floodwaters for more than a week. Beneath this shallow water, thousands of tonnes of vegetation is decaying and consuming oxygen.

“As the de-oxygenated water drains off the floodplain and into the creeks, it displaces all the good quality water and fish cannot breathe.”

The weekend’s hot weather has exacerbated the loss of oxygen.

The fish kill in Cudgera Creek has been extensive, resulting in the loss of many thousands of fish of different species, in particular smaller animals.

“It’s possible that larger fish have moved out of the creek into the ocean, but we have lost vast numbers of small prawns and the juvenile stages of many important species.

“It’s another big loss for our environment.

“There are still large areas of the floodplain inundated, in the catchments of Cudgera, Mooball and Cudgen creeks. While it is likely that we have seen the worst of it at Hastings Point, there is a significant risk that a similar event will play out at Kingscliff and Pottsville.”

Council will work with NSW Department of Fisheries to investigate and document this event and its cause.