Surface runoff is considered as the water flow that occurs when anything enters the ocean from rain, or other sources that flow over the land. This is one of the major components in marine pollution. When a runoff occurs on surfaces before reaching a channel it is called a nonpoint surface. When a nonpoint surface contains contaminants, the runoff is then called nonpoint source pollution. When these runoffs flow along the ground, it can pick up many things like: pesticides, fertilizers, petroleum, etc. Those become nonpoint source pollution.
Pollution from land-based sources is a major cause of coral reef degradation throughout the entire world. For example, in the Caribbean, about 80 percent of ocean pollution is caused by activities on land. When human population grows in coastal areas it increases runoff from land. Runoff usually brings big quantities of sediment rom land-clearing, high levels of nutrients that come from sewage outflows and agricultural areas. (Includes petroleum products and pesticides) These sources are harming coral reef health.