Clearly, NPS pollution affects coastal waters when contaminated rain water and snow melt run directly into the ocean or into other coastal waters, such as estuaries and salt marshes. Even rain and snow that fall many miles inland, however, can impact coastal waters by carrying NPS pollutants to rivers that ultimately run to the sea. Consequently, all activities in coastal watersheds (the geographic area from which water drains into coastal waterbodies) can cause coastal NPS pollution problems.

Coastal waters, therefore, are affected by the activities conducted within a very large land area. In Massachusetts, for example, the coastal watershed includes just over half of the state. In addition, the coastal regions of the United States are the most heavily populated areas of the country, which further heightens the problem of coastal NPS pollution.

Contaminants released into coastal waters because of NPS pollution cause many problems. For example, beaches must be closed to swimming when bacteria reaches certain levels in the water. Nonpoint sources of bacteria include boaters, farm animals, failed septic systems, and stormwater runoff. In addition, when pesticides and other chemicals get into the marine environment, they reduce the productivity of coastal habitats, such as estuaries. Because estuaries serve as the breeding grounds for fish and other wildlife, commercial fisheries are affected.

In Massachusetts, one of the most costly results of coastal NPS pollution is shellfish bed closings. Over the past fifteen years, shellfish bed closings have increased dramatically and many of these closings appear to be the direct result of NPS pollution from septic systems and from domestic and farm animals. Because they are filter feeders, shellfish are very sensitive to water pollution. As they feed, they filter contaminants and bacteria out of the water and often store these substances in their body tissue. Consequently, the contamination of shellfish with bacteria from human and animal wastes is a serious health threat. Once bacterial levels in coastal waters reach certain levels, the shellfish beds must be closed, preventing people from harvesting these resources.

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Published: October 1994