The jet ski, which is used by lifeguards to patrol the area around Penguin Island, was taken from a sea container on Arcadia Drive around 2.30am on March 19.
A Surf Lifesaving WA spokesperson said the theft was disappointing.
“It is disappointing that an individual, or individuals, would steal these items from a not-for-profit organisation that dedicates its resources to protecting the community,” they said.
“Penguin Island in particular has been the site of many rescues over the years and this equipment is vital in enabling our lifesavers to perform their jobs and ensuring additional lives are not lost there.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000.