EPA investigate dead fish found at Cooks River
Authorities are investigating why a huge amount of dead fish have washed up alongside an inner-west Sydney river. An expert has suggested two concerning reasons for the deaths — which come almost a year after something similar occured.
The Express
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Authorities are investigating the deaths of more than 100 fish on the Earlwood side of the Cooks River.
It comes almost a year to the day after 65 fish - mainly bream, mullet, luderick and flounder - were found dead at the same river.
While most of the dead fish - mainly mullet - were found on February 3, three were seen the day before. The EPA is investigating the fish deaths, along with Sydney Water.
While the Cooks River attracts hobby fishermen, the fish are not fit to eat, according to the Department of Primary Industries, because of the high levels of pollutants in the water.
According to Cooks River Alliance Executive Officer Sue Burton, fish kills can occur at any time but are more likely to occur either in summer, following sudden changes in daily temperature or after big storm events.
“The fish kill could have been caused by pollution or by last weekend’s intense heat or the downpour,” Ms Burton said.
“The rain dumps large quantities of stormwater into the river from street gutters along with all the litter and pollutants.
“This can rapidly change the water temperature, reduce oxygen and cause sewer overflows.”
She said based on the results of the EPA’s laboratory analysis, it was not possible to say what caused the fish kill last year.
Professor Stuart Khan of the School of Civil and Environmental Engineering at UNSW Sydney, said there could be two reasons for the deaths.
“There could the release of a toxic chemical like ammonia which is common from leaking sewage,” Prof Khan told The Express.
“The second reason could be due to the lot of organic matter like leaves, dead plants, etc which come through the storm drains or are washed into the river during the heavy rains and storms.
“It usually happens after a drought like we have experienced because the leaves and dead organic material accumulate in the storm water system.
“The bacteria, which live in the river, will break down the organic material but will consume Oxygen while doing it.
“This will lead to low levels of oxygen in the river which will affect and suffocate the fish.”
Prof Khan said since the Cooks River is a rather small waterway, it will eventually be flushed down to Botany Bay.
He said one way to boost the oxygen levels quickly will be to pump air into the river but it was an expensive process.
However, Prof Khan said there were simple tests, including probes, which can be done to measure dissolved oxygen concentrations in water, which should be done first.
The Cooks River Alliance, including the councils of Canterbury Bankstown, Bayside, Inner West and Strathfield share responsibility for the Cooks River with the EPA and Sydney Water.
The 23km Cooks River starts at Graf Park, Yagoona, and travels northwest through to Chullora. It then turns southwest before flowing into Botany Bay at Kyeemagh, next to Kingsford Smith Airport.
Anyone seeing dead fish at the river, are urged to report it to the EPA (131 555) or NSW Fisheries (1800 043 536).