Western Australian wildlife rangers are searching for a dolphin which appears to have had a T-shirt or singlet deliberately pulled over its head.

A member of the public saw the bottlenose dolphin swimming in Koombana Bay on Australia Day and reported it to the local Dolphin Discovery Centre.

In photos, it can be seen with a T-shirt or singlet around its body.

The Department of Parks and Wildlife (DPaW) believes it was done intentionally and could have been catastrophic.

"Dolphins are quite playful but it's unusual for them to be able to swim through something like that and get it sort of stuck," the department's Pia Courtis said.

"Thankfully for it, it's on the other side of its blowhole and its pectoral fins are out so it can still swim.

"But if it was done by somebody it's not great, and penalties under the Wildlife Conservation Act, [the] maximum penalty's about $4,000."

DPaW has urged members of the public to report any further sightings.

The shirt is covering the dolphin's dorsal fin, so officers could not tell if it was tagged or identify it from a set of local dolphin photos.

People are urged not to feed or touch dolphins or approach them in boats.