Surface water

Areas of surface water on Cape Cod and the Islands include salt marshes; freshwater marshes, bogs, and ponds; and small streams. Cape Cod and the Islands have no large streams on because of the high permeability of much of the unconsolidated materials. Precipitation that is not transpired by plants or evaporated largely infiltrates the ground with little or no direct surface runoff. Unlike most other basins in the State where groundwater mainly discharges to bodies of fresh surface water, much groundwater on the Cape Cod and the Islands discharges directly to the ocean and its bays.

Cape Cod has 353 lakes and ponds, 206 of which are at least 10 acres in area. Three lakes are larger than 500 acres: Long Pond in Brewster and Harwich (743 acres), Mashpee and Wakeby Ponds in Mashpee and Sandwich (729 acres), and Chequaquet Lake (Wequaquet Lake, Great Nine-Mile Pond) in Barnstable (654 acres).

Martha's Vineyard contains 62 lakes and ponds, 38 of which cover at least 10 acres. Six of these lakes are larger than 500 acres: Edgartown Great Pond in Edgartown (1,157 acres), Tisbury Great Pond in West Tisbury (772 acres), Sengekontacket Pond in Edgartown (716 acres), Menemsha Pond in Gay Head (640 acres), Squibnocket Pond in Chilmark and Gay Head (609 acres), and Lagoon Pond in Tisbury (535 acres). Nantucket has 28 lakes and ponds, 12 of which are at least 10 acres in area, and the Elizabeth Islands have 13 lakes and ponds, five of which are 10 acres or larger. The largest lake on Nantucket is Sasachacha Pond in Nantucket (276 acres); the largest lake on the Elizabeth Islands is Cuttyhunk Pond (100 acres).

Most lakes and ponds on the Cape and Islands are located in kettle holes on outwash plains and are surface expressions of the water table. At these locations, the altitudes of the pond surfaces closely match those of the water table. Lakes and ponds on the Cape and Islands are commonly used for irrigation, recreation, and fishing, but, with one exception, are not used for public-water supplies. The exception is Long Pond in Falmouth on Cape Cod, which is a part of that town's public water supply.