Marine hazards are a major concern for seafarers and can include both natural and man-made dangers. Two of the most common marine hazards are reefs and SHOALS. Reefs are underwater formations of rocks, coral, or sand that can be hazardous to ships due to their shallow depths. SHOALS are similar to reefs but are composed of sand or gravel and are usually found in shallow waters. Both of these hazards can cause serious damage to vessels if they are not navigated around properly.