MORE than 600 dead fish were found in the Swan River near the Garratt Road bridge this week.
Mostly bream, they were reported around the bridge and upstream on March 6, with the WA health department warning against fishing or even touching the water.
The health department says the cause and extent is still being investigated, but “significant rainfall and increased flows from the Avon River may have contributed to the fish kill. An increased amount of debris is also expected to float downstream in coming weeks following the large rainfall event.”
The dead fish were gone as of Monday March 8 and signs warned “this water may cause ill effects to human and animals” and urging “no direct water contact activities”.
The signs were few and far between; a seasoned fisher named Mitch didn’t spot them, but noticed an unusual orange tint to the water as he threw in a line.
He had some luck upstream of Garratt Road Bridge, pulling in two bream, saying his catch seemed unaffected and would make a good meal.
“Look – healthy, strong,” he said despite the warning.
Mitch pointed out the water was the same earthy colour he recalled during a 2012 fish kill, when some 14,000 succumbed to algal blooms.
Algal blooms have also contributed to dolphin sickness and deaths – along with chemicals – while last year Murdoch university researchers linked high rainfall events to a deadly skin disease on the mammals likened to being burned by acid.
After the 2012 die off the Swan River Trust prepared a report identifying a tangled web of problems. The river’s catchment area has been cleared for agriculture and development letting more contaminants and algae-causing nutrients flow downstream after rain.
That’s compounded by urban areas using chemicals and fertilisers, though Bayswater council’s won commendations for its efforts to treat stormwater before it hits the river. And the lower overall rainfall means reduced “environmental flow” to keep it healthy.
The SRT prepared a detailed strategy to fix the issue in 2015, tasking several state departments to take action, but the most recent progress report from August 2020 reveals several unfinished items.
Delayed or “at risk” items include managing “environmental flows” (a lack of flow let the 2012 algae sit around for months), monitoring contaminants, and research to investigate threats to the river’s ecosystem.
For now the potential spread of the fish kill is being monitored and anyone who sees dead or sluggish fish in other areas of the river are asked to call FishWatch on 1800 815 507.