Construction Sign

The Great Miami River Watershed is located in the southwest portion of Ohio.  This system includes the Great Miami, Stillwater, and Mad Rivers.  The drainage area of these systems in Ohio is 4,277 square miles.  Total drainage area including that portion in Indiana is 5,702 square miles. The Great Miami River Watershed includes all or part of 15 counties with the headwaters in Hardin and Auglaize counties and the mouth in Hamilton County.

Interstates 70 and 75, two of the nationís longest Interstate highway systems, intersect just north of Dayton.  Dayton, with a population of 190,000, is the largest city within the watershed.  Other major cities within the watershed exceeding 50,000 population include Springfield, 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 waterways in the watershed.

The following table is a summary of land use information for the watershed, provided by the Ohio Department of Natural Resources.  The data was obtained by scanning satellite imagery.

Land Use



Agriculture 80.3
Shrub/scrub 1.0
Wooded 11.7
Open Water 1.2
Non-forest Wetlands 0.6
Barren 0.2
Total 100.0

Some of the most significant water resource features in the watershed are the Stillwater Scenic River, the Great Miami buried valley aquifer, the five major dams (dry) and flood protection system of Miami Conservancy District (MCD), and Indian Lake, a remnant of the Miami-Erie Canal system and one of the largest lakes in Ohio.

Surface Water

There are 2,360 miles of rivers and streams in the Great Miami River Watershed.  Water quality in the watershedís rivers and streams has shown strong improvement over the last 20 years.  The following table provides attainment data collected by Ohio EPA in its stream surveys (1,063 miles assessed):



Full 427.3
Threatened 40.3
Partial 309.5
Non-Attainment 285.3
Total Miles Assessed 1063.0

The improved quality of the surface waters in the watershed, in addition to the existence of several major lakes, provides many opportunities for water-based recreation.  Boating, swimming and fishing are a few of the many activities enjoyed on Acton Lake, Indian Lake and Lake Loramie.  The cold water habitat of the Mad River is one of the few trout fishing streams in Ohio.

Upper Great Miami Watershed


Lower Great Miami Watershed

Mad River Watershed


Stillwater Watershed


The Miami Valley is blessed with one of the largest and most productive aquifer systems in the country.  The Great Miami buried valley aquifer consists of ancient river valleys filled with permeable deposits of sand and gravel capable of storing vast amounts of groundwater. The buried valley aquifer has sustainable yields of 500 to 3,000 gallons per minute. This aquifer system was designated by US EPA as a Sole Source Aquifer in 1988.  An estimated 97% of the population in the watershed relies on groundwater for their drinking water supply.

Geology and Soils

The geology of the watershed consists of bedrock underlying unconsolidated, surficial sediments containing Ordovician-age interbedded limestone and shale and Silurian-age shale, limestone and dolomite.  The dominant soils in this watershed are Miamian, Crosby, Russell, Kokomo, Blount, Pewamo and Glynwood.






Why Watersheds?

Watersheds provide critical natural services that sustain or enrich our daily lives:  they supply our drinking water, critical habitat for plants and animals, areas of natural beauty, and water bodies for recreation and relaxation.  Small streams are an important element of our local geography, and confer a strong sense of place to a community.

A watershed is the land around a river that drains water into the river.  Every tiny stream, every bubbling brook, and every ditch that carries water towards the river is part of the watershed.  Water will flow through forests and fields on its downhill journey to the river.  It will also flow over lawns, driveways and roads.  Eventually, the water ends up in the river.  All that land the water drained out of is a part of the watershed.

Everyone is part of a watershed.  Even if we donít live near a body of water, we live in its watershed, and our actions on that land affect water quality far downstream.

Watershed management is a holistic approach to water quality issues.  It recognizes and demonstrates the interconnectedness of land and water, surface and ground water, tiny streams and great oceans. 

The next time it rains, watch the water run off your roof, your driveway, down the street.  Everywhere you go, water is on its way to the nearest stream, lake or wetland.  Some of it soaks into the soil to become groundwater and slowly replenish streams and lakes.  Some runs overland.  When you add up all the land that catches water and drains it into the same waterway, you have a watershed.  Parts of fifteen counties in southwest Ohio drain to the Great Miami River and make up its watershed.  The Great Miami, in turn, drains into the Ohio River and is part of the Ohio River watershed.



This page is taken from: