The Charles River is a small, relatively short river in Massachusetts, USA, that separates Boston from Cambridge and Charlestown. It is fed by about 80 brooks and streams, and several major aquifers as it flows snakelike for 80 miles (129 km), starting at Echo Lake in Hopkinton, through 58 cities and towns in eastern Massachusetts before emptying into Boston Harbor. Its watershed contains 33 lakes and ponds. Despite the river's length and relatively large drainage area (308 square miles; 798 kmē), its source is only 26 miles (42 km) from its mouth, and the river drops only 350 feet (107 m) from source to sea. It is the most densely populated river basin in New England.