Hundreds of dead scaley mackerel are floating off a Western Australian beach, sparking an investigation and orders not to enter the water.

The fish kills were found between the Woodman Point Ammo Jetty and the Omeo Wreck, south-west of Perth, with onshore winds causing some to wash up on Coogee Beach.

A beach cleaning contractor was on site this morning to clear the fish, allowing the area to since reopen.

The WA Department of Primary Industries has collected information and samples to investigate the cause of death.

Due to advice from the department, the council also temporarily closed C.Y. O’Connor Beach, south of Catherine Point Groyne, this morning.

Up to 300 dead fish had washed up in the area.

A contractor will visit the site today to clean up the beach. 

Beachgoers are urged not to swim or fish in the North Coogee area due to a “high level of bacteria” and “objectionable odour”.

The dead fish should not be used for bait or consumption, either by people or their pets.

The WA Department of Primary Industries also warned that the fish may also wash up at other nearby beaches and to report any further sightings.