The mainland portion of the town is typical of Cape Cod, with several ponds, brooks, rivers, harbors, and inlets around the town. The town includes two narrow strips of land which serve as a barrier between the Atlantic and the mainland; the northern of these is the southern part of the Cape Cod National Seashore. There are several islands, including Strong Island, Tern Island (which is a sanctuary), Morris Island, Stage Island, and Monomoy Island, a island south of the corner of the town which is home to the Monomoy National Wildlife Refuge. Erosion has changed the region over the years—for example, an island named Slut's Bush once existed until it vanished under water by the mid 19th century.