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All About the Great Miami River Watershed


Originating upstream from Indian Lake, the Great Miami River flows 170 miles southwest to its confluence with the Ohio River west of Cincinnati. The Great Miami River Watershed drains all or parts of 15 counties and also includes the Stillwater and Mad rivers and Twin, Wolf and Seven Mile creeks. An estimated 97 percent of the population in the Great Miami River Watershed relies on groundwater for its drinking water supply. As a result of the watershed's glacial deposits, the Great Miami River and many of its tributaries flow over a buried valley aquifer consisting of thick deposits of sand, gravel, cobble and boulders. 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.

The water cycle is an unending and complex circuit that incorporates several different natural processes, including water evaporation, from the earth's surface, particularly from larger bodies of water.

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.

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.

More than 40 percent of streams and rivers, however, still do not meet Ohio's water quality standards. View infographic/factsheets on the right about each of the subwatersheds of the Great Miami River to discover more about the health of, and threats to, surface water.


With its abundant supply of high quality groundwater, the buried valley aquifer system 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.

The system underlies the river and streambeds, allowing plenty of opportunity for groundwater recharge. This essentially makes the aquifer an unending renewable resource.

The buried valley aquifer is a valuable natural resource and it is vital to manage it wisely. Proper management of this resource will ensure the aquifer continues to support and enhance the region's economy and quality of life. Highlights include:

  • Total aquifer storage of approximately 1.5 trillion gallons of groundwater.
  • Principal drinking water source for an estimated 2.3 million people.
  • Yields in excess of 2,000 gallons of water per minute are possible in wells near large streams.
  • Much of the groundwater maintains a constant temperature of 56 degrees Fahrenheit.
  • Appropriate use and proper protection will ensure that the aquifer is available as a long-term healthy fresh water supply.

The U.S. EPA designated the buried valley aquifer as a sole source aquifer in 1988. A sole source aquifer designation applies only to aquifers that serve as the sole or principal source of drinking water for an area. This designation signifies that contamination of the aquifer would create a significant hazard to public health.

As a result of this designation, all federally funded projects constructed near the aquifer, and its principal recharge zone, are subject to U.S. EPA review. This insures that projects are designed and constructed in a manner that does not create a significant hazard to public health.

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.

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.



Links to PDF Infographics with Great Miami River Watershed stream health ratings: