MORE than 700 dead fish have washed up at various locations in Cockburn Sound in the past week.
The Department of Fisheries is continuing to co-ordinate laboratory investigations on samples of dead fish collected.
But until results of the fish pathology and chemical analysis of water samples are available, the cause and potential impact could remain unknown.
Analysis of one affected fish’s tissue has indicated abnormal changes in the kidney and liver.
Other species are being examined to determine if it is a consistent finding.
All samples are being checked by the department’s Fish Health branch but results of the comprehensive tests may take up to a week to assess.
Biosecurity research scientist Michael Snow said a pollution event could not be ruled out, but preliminary laboratory findings suggested no evidence of algal blooms or disease being a contributing factor.
Results of water samples from the cities of Kwinana and Cockburn showed no bacterial water quality impacts.
“This fish-kill event has affected multiple species of fish and while disease also can’t be ruled out at this stage, the fact that multiple species have been involved suggests disease is less likely,” Dr Snow said.
The Department of Health has advised people not to swim in areas of water with large numbers of dead and decomposing fish, and not to fish in water with large numbers of dead fish.
They have also advised people not to collect or eat fish from Cockburn Sound and not to use dead fish for bait or food because of the risk of bacteria present.
Both Cockburn and Warnbro sounds have spawning closures on pink snapper fishing in place.
They are currently spawning in Cockburn Sound and until results from all analysis are available, the impact will remain unknown.