Parker River National Wildlife Refuge is a protected coastal sanctuary in northeastern Massachusetts that covers most of Plum Island and includes the mouth of the Parker River, much of Plum Island Sound, and marshland within the Great Marsh system. Established in 1942 to support migratory birds along the Atlantic Flyway, it spans 4,662 acres of beaches, dunes, marshes, mudflats, and other habitats that sustain more than 300 bird species and many other animals and plants. Human use once altered its farmland, dunes, marshes, and fish populations, but restoration and careful management have helped preserve it as both a major migration stopover and an important public natural area.