In response to severe flooding that had occurred in the Genesee Valley almost every seven years since the 1800s, Congress authorized the Mount Morris Dam project under the Flood Control Act of 1944. Completed in 1952 by the United States Army Corps of Engineers, the dam took four years to build at a cost of $25 million. Spanning 1,028 feet between canyon walls, it protects farm, residential, industrial, and commercial areas of the lower Genesee River Valley to Lake Ontario, including Rochester, and is estimated to have prevented more than a billion dollars in downstream damage. Known as a dry dam, it closes its nine floodgates only when needed, about 20% of the time, and then releases water at a rate intended to prevent downstream flooding once danger has passed. Impounded water has greatly altered habitat behind the dam, with settled sediments covering rock bars as far south as St. Helena and reaching depths of more than 50 feet at the dam. The structure is the largest concrete, gravity, dry dam east of the Mississippi River, rises 245 feet above bedrock, stands 760 feet above sea level at its spillway elevation, has a 550-foot-wide spillway, includes a six-story operations tower, and contains almost three-quarters of a mile of passageways for gate controls, pressure gauges, pumps, elevator shafts, and stairways. The Mount Morris Dam and surrounding area are owned and operated by the U.S. Army Corps of Engineers.
