Delayed response to fish kill prolonged disaster, says expert

Three weeks on from record fish kills at Menindee, fish are still gasping for air, as water testing shows high nitrogen and phosphorous levels were well above guideline levels.

Millions of fish died in a mass fish kill in Menindee in March. Picture: Michael Minns

Results from water samples taken during Menindee’s mass fish kill show nitrogen and phosphorous at levels much higher than guidelines allow, as fish continue to struggle in the Darling-Baaka three weeks on from the event.

The NSW Environment Protection Authority released the results on April 6 — more than two weeks after samples were taken on March 21.

They showed total nitrogen eight times higher than guideline values for lowland river ecosystems, and total phosphorous 11 times higher.

“The water samples from 21 March show high levels of ammonia, nitrite and nitrate, and there is a potential for harm to aquatic organisms,” the EPA wrote in a statement uploaded to its website.

Samples showed copper levels in the water were “above the level set to protect water life but well below the level harmful to fish”. All other metals were under levels set to protect water life and no pesticides were detected in the water.

The samples were collected by WaterNSW five days after the fish kill event started on March 16. Nutrient levels at the immediate onset of the event are not known, but a water quality report released by the NSW Department of Environment and Planning on 2 March said nitrogen and phosphorous were at “high concentrations”.

Menindee resident Graeme McCrabb says the fish kill was “100 per cent man made”.

Regular testing at Weir 32, downstream from Menindee, showed dissolved oxygen in the water dropped to zero on March 19 and stayed below 2mg/L — the lowest value fish need to survive — until March 23. A clean-up of the dead fish did not start until March 22.

Experts say a slow response by authorities to cleaning up the rotting fish likely prolonged and exacerbated poor water quality triggered by flooding upstream, while the closure of weir 32 meant fish were unable to escape to better quality water.

University of NSW professor of environmental engineering Stuart Khan said dead and decomposing fish that weren’t removed from the river quickly would have added to the nutrient load.

“Once you have a fish kill, and the fish start to be biodegraded, not only do they release nutrients, they’re also a source of organic carbon, so they also perpetuate more bacterial activity and more deoxygenation as the fish carcasses rot,” he said.

“The only way that you could mitigate that would be to try and pull out those dead fish as quickly as possible.”

At the time of the fish kill, Fire and Rescue NSW told media a large-scale clean-up did not get underway until March 23 due to the complexity of a multi-agency operation and the remote location.

NSW environment minister Penny Sharpe said on Friday the government was finalising the details of an independent inquiry into the fish deaths at Menindee and “will have more to say on this matter soon”.

Menindee resident and water advocate Graeme McCrabb said on Monday fish were still dying and struggling for air in the river.

He said he and other Menindee residents had been warning authorities since mid last year that water measurement upstream of Menindee was “inadequate”. Additional river gauges and water quality monitoring was needed upstream so authorities had a clear picture of how much water was heading downstream and what quality it was, he said.

“It is 100 per cent a man-made fish kill,” Mr McCrabb said.

The NSW Department of Planning and Environment said in a statement it planned to install new equipment to monitor dissolved oxygen levels at Nelia Gaari, Lake Wetherell, Railway Bridge, Menindee Town, Weir 32 and Pooncarie.