The deaths of thousands of fish and marron in the Collie River were not caused by pollution – but by freak weather conditions.
South West people were warned not to eat or handle fish found dead after an estimated 3000 marron and fish were reported crawling out of the Collie River and dying on its banks.
The Collie Mail spoke with Collie River researcher and activist Ed Riley who said water testing before and after the storms showed no increase in salinity.
“We can allay any public concerns - death of river life at Buckingham and Coolangatta cannot be attributed to mine water that has been discharged into the river,” he said.
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Mr Riley said the cause of the deaths was due to natural causes.
“The storms created an injection of warm water into the river system,” he said.
“This water sucked out the oxygen and stirred up nutrients in the river, which suffocated the marron and fish.”
Some marron made it out of the water only to be picked off by predators, while others were able to recover and re-enter the water.
It is estimated that 3km of the Collie River was affected by the weather conditions.
Signs of dead and dying perch, cobbler, shrimp and marron were first recorded on Thursday evening, following severe thunderstorms.
The dead fish and marron were reported to the department of fisheries in the east branch of the Collie River, about seven kilometres east to north east of the Collie town site, by a member of the public on Friday, January 30.
Officers from the departments of water and fisheries attended over the weekend.
The department of water said initial estimates were about 3000 freshwater cobbler, night fish, marron and redfin perch species found dead in the eastern branch of the Collie River off Boys Home Road.
Department of water South West manager Adam Maskew said samples of dead fish were collected to undertake pathology tests, and water samples were also taken.
“We have responded quickly to this report following the state fish kill incident response plan and are working with fisheries to determine the possible cause of the deaths,” Mr Maskew said.
The Collie shire is also assisting the departments in the response.
Mr Riley said by Monday morning water conditions had almost returned to normal and while fish stocks have been depleted they are expected to recover quickly.
"The food chain should not be too severely affected," he said.
He said deaths of this scale last occurred 30 years ago.
"While it is safe to eat anything caught in the Collie River – fishers are urged not do eat anything that has washed up dead."
The health department advises against eating or handling of fish found in these circumstances or fishing or recreating in waterways during a fish kill or algal bloom event.
People are asked to report any fish deaths to Fishwatch on 1800 815 507.
Algal blooms should be reported to ALGALWATCH 08 6250 8064 (office hours).
Last week, the Bunbury Mail reported a department of fisheries warning about marron caught at Grimwade Large Dam near Balingup.
The Department of Fisheries has received scientific advice to provide preliminary identification of a worm found in cysts on the flesh of marron.
