Scientists investigating the deaths of more than 1,000 fish at Cockburn Sound, south of Perth, say early tests suggest environmental factors are most likely to blame, as they investigate fears the incident is affecting local birds.
The dead fish first washed up in late November.
This week there were more reports of large numbers of dead blowfish and snapper near the Garden Island Causeway and Point Peron boat ramp.
A local fisherman has posted photographs online of dead blowfish and a dead pelican found on the beach at Shoalwater, about five kilometres from Cockburn Sound.
The Department of Parks and Wildlife (DPAW) will collect the animal and have it tested.
However, the department said it was not unusual for it to respond to bird deaths, and it was too early to say whether it was connected to the fish deaths.
The department said it was not aware of any other recent bird deaths in the area.
Department of Fisheries researcher Dr Michael Snow said disease had been ruled out as a possible cause of the fish deaths.
Tests on the fish for more than 120 chemicals were still underway, but had so far not produced any results.
Dr Snow said the focus of the investigation was now on water quality.
“Growing evidence is indicating that it may well be a natural event,” he said.
“Algal blooms, anything leading to dissolved oxygen, or it could be an increase in turbidity.
“Anything that influences the gills of the fish as it swims through the water.”
Dr Snow said he was certain it was safe to swim in the area and also safe to eat fish caught in the affected waters.
2015 ABC