The Hudson River officially starts at Lake Tear of the Clouds in the High Peaks area of the Adirondacks. The river flows south for 315 miles (507km) to the Atlantic Ocean at New York City and eventually forms the boundary between New York City and New Jersey. The huge watershed of the Hudson covers about 13,350 square miles including most of eastern New York and small part of Vermont, New Jersey, and Massachusetts. While the northern part of the Hudson is clear and cold surrounded by forest and ancient metamorphic rocks, as the river nears the Mohawk lowlands, it changes to a pastoral terrain surrounded by farms with underlying sedimentary rocks. The erosion of the sedimentary rock makes the river water richer in calcium and other minerals. This area of the Hudson River has fourteen dams and industrial activities. When the Hudson passes over the Troy dam, it becomes an estuary. Some water for the city is drawn from the Hudson River in the area just north of Poughkeepsie. However, it represents just a small portion of the city's water supply.