Oradell Reservoir was formed by the Oradell Reservoir Dam placed on the Hackensack River, which was started in 1921 and finished in 1923. The reservoir is fed by the Pascack Brook and Dwars Kill in addition to the Hackensack River. The Dam has greatly reduced the amount of flooding in the eastern part of Oradell caused by the Hackensack River, though it also resulted in the loss of flora and fauna that depended on the fresh water that flowed down the river. Fed by rain from Hurricane Irene in August 2011, the water level in the reservoir was two feet above the top of the dam, allowing billions of gallons of water to flow over the dam and exacerbating flooding conditions in Oradell and New Milford.