The Big Darby flows across the southwestern section of the county. Already designated a State Scenic River, the Big Darby is being considered for National Scenic River designation. Parts of this watershed are considered to have an excellent and unique stream habitat, and this has helped promote continued emphasis in the Darby watershed on improved conservation measures to curtail erosion and surface runoff of sediment and agricultural chemicals. In 1991, a USDA Hydrologic Unit Watershed Project was initiated in the Darby Creek Watershed. The purpose of this project is to work with farm producers and other landowners to encourage the use of agronomic practices that will further improve the water quality of Big Darby.
Mill Creek runs from northwest to southeast across the central portion of the county.
Many other streams such as Rush Creek, Bokes Creek and Fulton Creek are also important. These and other smaller streams combine to make the total county stream length approximately 535 miles. Fishing and canoeing are the main recreational uses along the larger of these county streams. About 12 other human-made lakes ranging from 5 to 20 acres are located in the county. The majority of the ponds are filled by precipitation and runoff.