Ocean hazard is a term used to describe the various dangers that can be encountered when travelling in the ocean. Reefs, sharks and whirlpools are all examples of ocean hazards. A REEF is a ridge of rocks or coral that lies just below or above the surface of the water, making it difficult to navigate around. Sharks are large predatory fish that can pose a threat to humans and other marine life. Whirlpools are powerful currents of water that can pull objects and people into them.