Shark Island (Oman) is actually Fahal Island, a small island about two miles due north of Qurum in Oman. There is an annual open water swim, but swimmers can also hire a kayak (e.g. from Muscat Diving & Adventure Centre) for support.
Shark Island (Australia) is a dangerous reef break about 100 metres off Cronulla, New South Wales, Australia. It comprises a rock ledge that is fully exposed at low tide. The island is a well-known bodyboarding and surfing location. The wave can stand up fast and violently, making it difficult and dangerous.