The Genesee River receives drainage from about 2,500 square miles, including portions of Genesee, Livingston, Wyoming, Monroe, Allegany, Steuben, Ontario, Orleans, and Cattaraugus counties in New York, and Potter County in Pennsylvania. Its 157 mile-long northern journey begins at an elevation of 2,500 feet above sea level in the Allegheny Hills of Pennsylvania, flowing through the highly dissected Northern Allegheny Plateau to Letchworth State Park near Mount Morris in Livingston County (average stream slope of nearly 9 feet per mile), and then through the Lake Ontario Lowlands (average stream slope of 0.8 feet per mile), before flowing into Lake Ontario (elevation 247 feet above sea level) at the port of the City of Rochester in Monroe County, New York State.

The Genesee Basin contains a total of 5,048 miles of streams. The Genesee Basin also includes lakes, ponds, and reservoirs covering 13,288 acres. Of these lakes, the five largest – the Mount Morris Dam Impoundment, Canadice Lake, Conesus Lake, Hemlock Lake, and Honeoye Lake – represent over 80% of the total lake acres in the Genesee Basin.

The Genesee River has been shaped by its glacial history. By the time the last glacier permanently receded, around 12,000 years ago, the Genesee River’s drainage area had been well-established. Evidence of the early Genesee River’s size and eroding power can be seen today in the magnificent gorge at Letchworth State Park  near the Village of Mt. Morris, and in the river gorge downstream from High Falls in the City of Rochester.

Current land use within the watershed is approximately 52 percent agricultural, 40 percent forested, 4 percent urban, 2 percent wetlands or water, 2 percent other developed lands. The southern portions of the river basin in the Northern Allegany Plateau are dominated by forest and some agricultural land. Central and North Central portions of the River Basin are dominated by extensive agricultural development, primarily in support of dairy farming; however, orchard and vegetable crops are also grown. Within the basin, water resources are utilized to irrigate agricultural crops.

The Genesee River Basin has yielded enormous benefits to its residents, including a variety of land and water uses such as navigation, recreation, energy production, wildlife habitat; and fresh water for drinking, irrigation, industrial uses, and sanitation.