Saco Bay is a small curved embayment of the Gulf of Maine on the Atlantic coast of Maine in the United States. The name derives "from a map of the coastline made in 1525 by the Spanish explorer Esteban Gómez. He named the bay Bahio de Saco (Bay of the Sack)." Saco Bay is approximately 10 mi (16 km) wide, running from the Fletcher Neck (the Biddeford Pool peninsula) and the mouth of the Saco River in York County north to the Scarborough River and Prouts Neck in Scarborough, Cumberland County, Maine, approximately 13 mi (19 km) southwest of Portland. The shoreline of the bay makes the largest sand beach and salt marsh system in Maine and contains the longest unbroken stretch of beach in the state. Ecosystem Construction of a railroad causeway in the 19th century led to the closure of the Little River Inlet. This tidal re-entrant had formed the county line between York and Cumberland counties and the town line between Scarborough and Old Orchard Beach. Prior to its closure, the Pine Point region of Scarborough was a barrier island, the only one in Maine. Behind Pine Point is the state run wildlife management area for Scarborough Marsh. The marsh is 15% of the state's total tidal marsh area and the largest contiguous marsh in Maine. The state owns and manages a reserve, of which is salt marsh, about is upland habitats, with the remainder being other types of wetlands. The marsh is an excellent site for birding as 72% of the water dependent birds that can be found in Maine can be found at the marsh. The marsh is located within of two nationally significant seabird nesting islands. The marsh has been designated essential habitat for endangered piping plovers and least terns. The Maine Audubon Society maintains a center at the marsh from which visitors can do hikes or rent a canoe and paddle through the marsh. The U.S. National Marine Fisheries Service has designated Saco Bay as "essential fish habitat" for at least fifteen types of fish, including Atlantic salmon, hake, halibut, herring, and scallops. Stratton Island in the bay is a wildlife sanctuary owned and run by the National Audubon Society where multiple species of terns nest. Arctic, common, and roseate terns have been regulars, and in 2005 they were joined for the first time by nesting least terns. Sand movement and erosion The