|- location||Approximately 2 mi (3.2 km) northeast of Galion, Ohio|
|- elevation||1,190 ft (360 m)|
|Scioto River at Columbus|
|710 ft (220 m)|
|Basin size||543 sq mi (1,410 km2)|
It was originally called keenhongsheconsepung, a Delaware word literally translated as "sharp tool river", based on the shale found along its shores. Early settlers to the region translated this into "Whetstone River". In 1833, the Ohio General Assembly passed legislation intending to restore the original Native American names to some Ohio waterways, but mistakenly gave Whetstone River the name "Olentangy"—Delaware for "river of the red face paint"—which had actually belonged to what is now known as Big Darby Creek.
The Olentangy River rises in Crawford County approximately 2 mi (3.2 km) northeast of Galion, flowing through Galion and northwest towards Bucyrus, where it then turns south and flows through Eastern Marion County, Ohio (where it is still locally known as the Whetstone River) before flowing south into Delaware County. The river continues southward towards the communities of Delaware, Powell, Worthington, and the village of Riverlea, before reaching Columbus and the campus of 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. On January 13, 2005, Delaware Dam was nearly overtopped. The water level came within less than 1 foot of the top of the dam, requiring the main spill gates to be opened before it began dropping.
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 (and other communities beyond), draw the majority of their water supplies from the Olentangy system.
The Olentangy River has also been known as Keenhongsheconsepung, Oleutangy, Whetstone Creek, Whetstone River, and Whitestone Creek.
In 2012 the Ohio EPA and the City of Columbus began to remove some of the lowhead dams that cross the river. Work started with removing the 5th Avenue Dam. The river is now about half of its former width. Work continues to restore the banks and clean the area.
- U.S. Geological Survey. Blooming Grove quadrangle, Ohio. 1:24,000. 7.5 Minute Series. Washington D.C.: USGS, 1988.
- U.S. Geological Survey. Southwest Columbus quadrangle, Ohio. 1:24,000. 7.5 Minute Series. Washington D.C.: USGS, 1995.
- "Map of Ohio watersheds". Archived from the original on 11 March 2007.
- "The National Map". U.S. Geological Survey. Retrieved 14 February 2011.
- Lentz, Ed. "Local river names have convoluted origin". This Week Community Newspapers. Gatehouse Media. Retrieved 16 October 2018.
- "Delaware Dam nearly overtopped on January 13, 2005".
- "Olentangy State Scenic River".
- U.S. Geological Survey Geographic Names Information System: Olentangy River
- "Removing the Fifth Avenue Dam". Retrieved 30 January 2017.
- "5th Ave Dam Project". Retrieved 30 January 2017.
- EPA, OW, US. "Polluted Runoff: Nonpoint Source Pollution" (PDF). Retrieved 30 January 2017.
- "Jackson's Last Call". Chicago Tribune. Retrieved 2 August 2017.
- Friends of the Lower Olentangy Watershed
- Delaware Dam level and outflow graph
- Olentangy River Level Gauge at Worthington, OH