A Perth photographer has captured the rare moment a double rainbow formed over the ocean off Yanchep on Saturday morning.

Bob Ellisdon, owner of Outback Bob Photography, told WAtoday he saw the rainbow forming from his house and rushed to capture the phenomenon.

Bob Ellisdon captures the double rainbow off WA's coast.

"I was out the front yard and saw a rainbow forming, so I jumped in the car and went down the beach," he said.

"I live in Yanchep, so I went to Fisherman's Hollow beach and it turned it on."