Cochituate, Lake (ko-CHIT-choo-wuht), reservoir, at Natick, Middlesex co., E Mass., on Sudbury R., 16 mi/26 km WSW of Boston; c.3 mi/4.8 km long; 42°18'N 71°22'W. Originally part of water-supply system for Boston area. Cochituate village to NE. Lake Cochituate State Park on E shore.