Part of the New York City water supply system, it was formed by impounding the East Branch of the Croton River.

Forming part of the Croton Watershed, it was placed into service in 1891, and lies some 35 miles (56 km) north of the city, in the southeast corner of Putnam County.

The East Branch Reservoir has a surface area of 525 acres (2.12 km2), reaches a mean depth of 32 feet (9.8 m), and holds 5.2 billion US gal (20 million m3) at full capacity.

Water from the aqueduct flows into the Jerome Park Reservoir in the Bronx for daily distribution.

One of two double reservoirs in NYC's system, it is connected to the Bog Brook impoundment via a 1,778-foot (542 m) tunnel.