Lake DeForest, also called DeForest Lake,[2]: 195–213  is a reservoir in Clarkstown, New York, created in 1956 by impounding the Hackensack River, which is a principal part of the water supply for Rockland County, New York and Northern New Jersey, mainly Bergen and Hudson counties.

[2]: 212  The lake is traversed by a causeway carrying Congers Road (CR 80).

[2]: 195–213 Adrian Leiby's monograph, The Hackensack Water Company, 1869-1969,[2] describes the conception of the lake (owing chiefly to George F. Wieghardt, chief engineer from 1938 to 1954);[2]: 195–213  the sense that the proposed lake needed to be built soon, before any ill-advised new housing developments on the swampy lowlands would preclude it;[2]: 195–213  and unrest among the public fueled by fears the proposed lake was a plan by New Jersey thieves to steal water from New York state or to create miles of "smelly mud flats" in Clarkstown.

[2]: 195–213  By the time of a severe drought in 1963-65, Leiby noted, public approval of the attractive lake and the water security it provided was nearly universal;[2]: 221  writing in 1969, he said, "Twelve years later it is hard to believe that there is a single person in the County who would willingly see DeForest Lake drained and its land filled with development houses.

Henry's father, Robert W. DeForest, had led the Hackensack Water Company from 1881 to 1926.