Marine hazards are a type of environmental hazard that can be found in the ocean. A REEF is an underwater formation of rocks, coral, or sand that can pose a danger to ships and other vessels. An EDDY is a swirling current of water that can cause boats to become stuck or capsize. A SANDBAR is a ridge of sand that can be submerged or exposed depending on the tide, and can be hazardous to navigation. A SHOAL is a shallow area of water that can be difficult to navigate due to its depth. All of these marine hazards can be dangerous to ships and other vessels, and should be avoided when possible.