UPDATE: WA Police have confirmed the investigation relates to a property search, and no further details would be released.
Peel and Fremantle Water Police divers are searching the Mandurah estuary on Thursday, as part of an "ongoing investigation".
Police have sectioned off part of a jetty near the Eastern Foreshore for the diving search of the area.
Officers are on the jetty issuing instructions and the Peel Water Police boat is stationed nearby.
Fremantle Water Police Acting Sergeant Adam McGregor said he could not speak about the details of the search.
"It's an ongoing investigation," he said.