Maintenance workers have found a live carpet or wobbegong shark inside the seawater intake tank of the Southern Seawater Desalination Plant in Binningup, according to Water Corporation, operator of the plant.

Water Corporation spokeswoman Clare Lugar assured that water quality has not been compromised and the shark will be removed from the 22-metre deep tank at the end of a 500-metre pipeline where seawater passes.

Lugar said the shark had most likely entered the station via the pipeline during the plant's construction while a grated screen was not in place.

She said it was not immediately detected because it is in a part of the pipeline that could not be visually checked for safety reasons.

"It would not be possible for a similar shark to enter the station again via the pipe as the screen would now prevent this," said Lugar.

The plant, located about 150 kilometres south of Perth, opened in September at reduced output. When completed next year, it will supply water to the state capital Perth, as well as the nearby regional city of Bunbury.

A carpet shark