A shark warning has been issued after a swimmer was bumped by a reported 3.5 metre bull shark in Canning River. A shark warning has been issued after a swimmer was bumped by a reported 3.5 metre bull shark in Canning River. Credit: AdobeA shark warning has been issued after a swimmer was bumped by a reported 3.5 metre bull shark in Canning River. A reported 1.7 metre bull shark was spotted by a member of the public at nearby Gentilli Way Boat Ramp just five metres offshore early Thursday morning. Swimmers were last year warned of increased shark activity in the Perth river system after more bull sharks were spotted near the old Fremantle traffic bridge.