A large-scale fish kill on Perth's south coast was caused by an algal bloom, possibly associated with low levels of oxygen in the water, the Department of Fisheries says.
More than 1500 dead pink snapper and blowfish began washing up on the shores of Cockburn Sound last month.
Supervising scientist Michael Snow said satellite data also showed an increase in surface water temperature at the time, which may have contributed to the bloom.
"Investigations have included screening for a wide range of over 120 algal toxins and industrial contaminants including heavy metals, fertilisers, pesticides and hydrocarbons," Dr Snow said in a statement on Tuesday.
"Other government agencies have also pursued and eliminated a number of other possibilities."
Dr Snow said Fisheries would continue to monitor fish stocks to assess the long term implications of the bloom.
He said algal diatoms, similar to the diameter of a human hair, naturally occurred in all marine and estuarine environments and were not harmful to humans.
Dr Snow said the Department of Health had confirmed the Sound was safe for fishing and swimming, but seasonal restrictions on pink snapper fishing remained in place due to spawning.
A ban on crab fishing remains due to stock declines.
The breakthrough was announced after the opposition accused the state government of not being transparent enough about the incident.
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