A watershed is an area of land that drains water and snowmelt into a specific waterbody. Every body of water has a watershed.
The Great Miami River Watershed drains all or parts of 15 counties in southwest Ohio, including the Stillwater and Mad rivers, and Twin, Wolf and Seven Mile creeks, into the Great Miami River.
Originating upstream from Indian Lake, the Great Miami River flows 170 miles southwest to its confluence with the Ohio River west of Cincinnati. The total drainage area of the watershed in Ohio is 3,946 square miles; the entire watershed, including the Whitewater River in Indiana, drains 5,702 square miles.
Surface Water
There are more than 6,600 miles of rivers and streams in the Great Miami River Watershed. Since the Clean Water Act was passed in 1972, regulations have limited the discharge of pollutants into waterways, so the water quality in the watershed has shown strong improvement.
More than 40 percent of streams and rivers, however, still do not meet Ohio's water quality standards. View infographic maps below about each of the subwatersheds of the Great Miami River to discover more about the health of, and threats to, surface water:
Groundwater & The Buried Valley Aquifer System
Not all rain or snow that falls within the Great Miami River Watershed flows directly into the Great Miami River. Some of it seeps into the ground and into an underground reservior of water called the Great Miami Buried Valley Aquifer (GMBVA). With its abundant supply of high quality groundwater, the GMBVA is the most important aquifer in southwest Ohio. This system consists of highly permeable sand and gravel deposits as thick as 200 feet that can store a great deal of groundwater. An estimated 97 percent of the population in the Great Miami River Watershed relies on its groundwater for their drinking water supply.
Recreation
These healthy waterways, in addition to the existence of several major lakes, provide many opportunities for water-based recreation. The cold-water habitat of the Mad River provides one of the few trout fishing streams in Ohio, and the scenic beauty of the Stillwater River attracts fishermen from all over the country. Boating, swimming and fishing are a few of the many activities enjoyed on Acton Lake, Indian Lake and Lake Loramie.
Learn more about recreation opportunities
Land Use
More than 70 percent of the land is used for agriculture, primarily row-crop production of corn, soybeans and wheat. Residential, commercial and industrial uses cover about 12 percent of the watershed; forests cover about 4 percent; and water bodies or wetlands cover about 1 percent.
Population
The watershed has a population of 1.3 million people with more than 75 percent of the population residing in urban areas. According to the U.S. Census Bureau population estimates, Dayton is the largest city in the watershed with 137,000 people. Other major cities within the MCD flood protection system exceeding 50,000 people include Hamilton and Middletown. Cities with more than 20,000 people include Piqua, Troy and Fairfield. Each of these major population centers is located adjacent to one of the rivers or streams in the watershed.
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