THOUSANDS of fish have died in the Vasse estuary at Wonnerup.
They were discovered on the weekend.
The cause of the deaths is not yet know, but is thought it may have been connected with constant rain in the preceding two days and the fact that the floodgates were closed.
Other water species such as crabs have also died.
Conservationists Phillip Moore and Beverley Sykes, who were among the first to find the fish on Saturday morning estimate that between 7000 and 8000 fish have died - the major kill being in a lagoon near their property.
“They are mainly black bream and mullet - various other species including Blue Manna crabs also died,” Phillip said.
“Generations of fish have died in this episode.
“By Sunday evening more fish - far worse than what we saw on Saturday morning, had surfaced,” he said.
He said they now faced a massive cleanup of the dead fish.