Investigation into “hundreds” of dead fish in Collie River underway

An investigation has been launched into the deaths of hundreds of fish in the Collie River last week.

While the majority were black bream, whiting, yellow-eyed mullet, tailor and blowfish were also found floating on the surface of a 5km stretch of the river near Australind, in an area known as The Elbow.

Locals on Thursday made the grim discovery and reported it to authorities, with Department of Water and Environmental Regulation officers arriving to take samples the following day.

Eaton fisherman Garry Henneberg said fish were floating in the water “every 10m” when he was there on Saturday.

He said he had seen something similar in 2015, but noted the lack of species evident was “very strange,” with all of the dead fish appearing to be black bream.

Fisheries officers from the Department of Primary Industries and Regional Development took further samples over the weekend — which will be tested for diseases — and inspected the area.

The recent rain and high tides may be contributing factors but the samples will undergo laboratory testing in order to determine what has caused the fish kill.

A Department of Water and Environmental Regulation spokesperson said it was not the first time fish kills had been seen at this time of the year.

“We do see kills like this at this time of year in the lower reaches of slow moving, tidally-influenced, river and estuary systems on the coastal plain,” they said.

“Often generally poor water quality after a long dry season and little to no rain causes generally stressful conditions for fish over a period of time.”

Sometimes rain washes in organic material, which can cause increased bacterial activity and can lower the dissolved oxygen to the point where fish can die from hypoxia or result in a bloom of potentially icthotoxic algae species.

In both cases the high tide contributes due holding back the normal flow of the river which would improve the water quality conditions or dilute the algal species.”

Until the investigation is complete, people are urged not to swim or fish in areas where there are large numbers of dead fish, not to collect, eat or use as bait any fish from water near a fish kill, and not to let pets near the fish kill.

The situation will continue to be monitored and anyone who sees a fish kill is urged to report it to the FishWatch 24-hour hotline on 1800 815 507.