The Olentangy River originates approximately 3 miles south of Bucyrus in Crawford County. It flows through the communities of Delaware, Powell, Worthington, and the campus of The Ohio State University, before joining with the Scioto River in downtown Columbus.

The Delaware State Park Reservoir, also known as Delaware Lake, was constructed along the Olentangy River in 1951. The reservoir is located 5 miles north of the City of Delaware, and was built by the U.S. Army Corps of Engineers for flood control purposes.

The Olentangy River was named by a legislative act in 1833 that restored Native American names to rivers in Ohio. The word Olentangy translates as "river of red face paint." The Olentangy River's name is a good match with one of its tributaries, the Whetstone Creek. The native inhabitants of the area used the shales in the creek as whetstones to sharpen their tools. (Ohio Department of Natural Resources, Division of Natural Areas & Preserves)

The Olentangy River is the primary source of drinking water for much of Delaware County. Both the City of Delaware and Del-Co water company, the supplier of drinking water to most of rural Delaware County, draw the majority of their water supplies from the Olentangy system. Twenty-two miles of the Olentangy have been designated a State Scenic River by the Ohio Department of Natural Resources, Division of Natural Areas & Preserves.

• Drainage Area: 81,142 acres (127 square miles)
• 132 miles of streams
• Contains Delaware Lake (1159 acres)