The Kensico Reservoir is a reservoir located in the towns of Armonk (North Castle), Harrison and Valhalla (Mount Pleasant), New York. It was formed by the old earth and gravel dam, built in 1885, which impounded waters from the Bronx and Byram rivers, and supplied about 18 million gallons daily. The construction of a new masonry dam in 1915, replaced the old dam, and expanded the water supply by bringing water from the Catskill Mountains over a distance of more than 100 miles. It is about 3 miles (5 km) north of downtown White Plains, New York, and about 15 miles (24 km) north of New York City. The reservoir serves mainly to store the waters received from the Catskill Mountains west of the Hudson River. Along with the West Branch Reservoir and Boyds Corner Reservoir, it is one of only thre