The Cannonsville Reservoir is a reservoir in Delaware County, New York, that was formed by the Cannonsville Dam at the west end of the reservoir, impounding over half of the West Branch of the Delaware River. It is the westernmost of New York City's reservoirs, being at the western portion of the Delaware Watershed. Placed in service in 1964, it is the most recently constructed New York City-owned reservoir. The town of Cannonsville was destroyed to make room for the reservoir.