Gain Creek is a river in the Capital Regional District of British Columbia, Canada. Located on southern Vancouver Island, it flows from its source to its mouth as a right tributary of Loss Creek.
Gain Creek begins at an unnamed confluence on the south slope of the San Juan Ridge at an elevation of . It flows southwest, and reaches its mouth as a right tributary of Loss Creek at an elevation of , south east of the settlement of Port Renfrew. Loss Creek flows to the Strait of Juan de Fuca on the Pacific Ocean.