The number of fish killed in the Vasse-Wonnerup Estuary this week has been revised to more than 10,000.
City of Busselton workers spent yesterday cleaning up the dead fish, mostly mullet, around the Vasse floodgate area.
The Department of Water says high levels of toxic algae are present in the waterway, which is likely to have caused the fish deaths.
The department says the oxygen levels, which were blamed for the fish kill of the same size last year, all appeared normal this time.
Findings of an independent review into the waterway’s management are set to be handed down this month.