The Oradell Reservoir was formed by a dam placed on the Hackensack River in Bergen County, New Jersey, completed in 1923. The dam is located in Oradell, but the reservoir also straddles the borders of Haworth, Emerson, Closter and Harrington Park.

The reservoir is fed by the Pascack Brook and Dwars Kill in addition to the Hackensack River.

Upstream from the Oradell Reservoir are three other reservoirs: Woodcliff Lake and Lake Tappan also in Bergen County and DeForest Lake in Rockland County, New York.

The Oradell Reservoir and its tributaries are protected with Category 1 water purity status in New Jersey.

The reservoir is managed by Uniter Water , a private utility. It provides drinking water for an estimated 750,000 residents of Bergen and Hudson counties.