"Cadborosaurus willsi", nicknamed "Caddy", is the name given to a sea serpent reported to be living on the Pacific Coast of North America. Its name is derived from Cadboro Bay in Victoria, British Columbia, and the Greek root word "sauros" meaning lizard or reptile. The animal is similar in form and behavior to various popularly named lake monsters such as "Ogopogo" of Okanagan Lake of British Columbia and to the Loch Ness Monster of Scotland.

There have been more than 300 claimed sightings during the past 200 years, including Deep Cove in Saanich Inlet, and Island View Beach, both like Cadboro Bay also on the Saanich Peninsula, also British Columbia, and also at San Francisco Bay, California.

Cadborosaurus willsi is said to resemble a serpent with vertical coils or humps in tandem behind the horse-like head and long neck, with a pair of small elevating front flippers, and a pair of large webbed hind flippers fused to form a large fan-like tail region that provides powerful forward propulsion.