Orleans is fortunate to have three major estuary systems: a set of three marshes off of Cape Cod Bay, Pleasant Bay - the largest estuary on Cape Cod, and Nauset Harbor/Nauset Bay/Town Cove.
Our estuaries provide nurseries and habitats for a large number of organisms, including fish, shellfish, terrapins, and eel-grass. They are highly productive growth environments. Migratory bird populations also make essential use of estuaries.
Estuaries form transition zones between river and saltwater environments. The waters are tidal, brackish or slightly salty, and high in sediments. The mixing of sea water and fresh water provide high levels of nutrients both in the water column and in sediment making estuaries among the most productive natural habitats in the world.
The banks of many estuaries are among the most heavily populated areas of the world, with about 60% of the world's population living along estuaries and the coast. As a result, many estuaries suffer degradation from a variety of factors including: sedimentation from soil erosion; overfishing; drainage and filling of wetlands; eutrophication due to excessive nutrients from sewage and animal wastes; pollutants from sewage inputs; and diking or damming for flood control or water diversion.