Genesee, river, 158 mi (254 km) long, rising in the Allegheny Mts., N Pa., and flowing through W N.Y. to Lake Ontario at Rochester; it is crossed by the New York State Canal System's Erie Canal. The Genesee valley is noted for its fertility and beauty. Along the middle Genesee is Letchworth State Park, with a gorge and several waterfalls. A dam and reservoir at Mt. Morris, N.Y., form part of a flood-control project. Rochester, on the lower Genesee, grew around two waterfalls that are used to produce hydroelectricity.