Sperm whale beached on a sandbar at Perth's Rockingham Foreshore unlikely to survive

A sperm whale seen close to swimmers off the coast of Perth at the weekend has today beached itself on a sandbar about 30 kilometres away.

The 15-metre whale was first spotted at Port Beach on Saturday, and then made its way to Coogee yesterday.

It was hit by a boat at Fish Rocks and was today stranded at Naval Memorial Park at the Rockingham Foreshore about 100 metres from the shore.

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A member of the public notified authorities about 5am and City of Rockingham Rangers closed the beach.

The Department of Biodiversity, Conservation and Attractions as well as rangers and marine mammal experts spent the day patrolling the beach to ensure the mammal was left alone.

"I think it's very unlikely given the circumstances and given the appearance and condition of the whale that it's going to survive," marine scientist Dr Kelly Waples said.

It is likely that the animal will be euthanised, however this will be a challenge in itself given how close to shore it is.

People have been urged to avoid the area, especially given it can cause further distress to the stranded whale.

A shark alert was also issued for the area and nearby Point Peron.

"It is possible the whale stranding will act as an attractant that could lead to sharks coming close in to shore along this stretch of coast," the alert said.

The beach will remain closed for the coming days.