Major Tributaries of the Ohio River: A Confluence Atlas

The Ohio River (981 mi / 1,579 km) forms at Pittsburgh from the Allegheny and Monongahela — then gathers water from a 204,000 mi² basin across 14 states. Here are its major tributaries in confluence order.

Upper Ohio (Pennsylvania / Western PA)

• Allegheny River (325 mi) — confluence at Pittsburgh (The Point). Largest by volume. NY/PA; Kinzua Dam.
• Monongahela River (130 mi) — confluence at Pittsburgh. North-flowing; WV/PA; navigable whole length.
• Beaver River (21 mi) — at Beaver, PA. Short but industrial (Beaver Valley).
• Youghiogheny River (134 mi) — near McKeesport, PA. "Yough" — whitewater, Ohiopyle Falls.

Ohio River Main Stem (West Virginia / Ohio / Kentucky)

• Muskingum River (111 mi) — at Marietta, OH. Lock/dam system (10); first US canalized river.
• Little Kanawha River (169 mi) — at Parkersburg, WV. Oil/gas history.
• Hocking River (102 mi) — at Hockingport, OH. Athens (OU) on tributary.
• Kanawha River (97 mi) — at Point Pleasant, WV. New + Gauley = Kanawha. Chemical industry.
• Guyandotte River (166 mi) — at Huntington, WV. Coal, Marshall Univ.
• Big Sandy River (29 mi) — at Catlettsburg, KY. Tug + Levisa forks; KY/WV/VA border.

Lower Ohio (Indiana / Illinois / Kentucky)

• Scioto River (231 mi) — at Portsmouth, OH. Columbus on Scioto.
• Green River (384 mi) — at Evansville, IN. Mammoth Cave drainage; locks/dams.
• Wabash River (503 mi) — at Shawneetown, IL. Longest Ohio tributary; IN/IL border.
• Saline River — minor, IL.
• Tradewater River — minor, KY.
• Cumberland River (688 mi) — at Smithland, KY. **Largest by drainage (18,000 mi²).** Barkley Dam (Lake Barkley).
• Tennessee River (652 mi) — at Paducah, KY. **Largest by discharge (68,000 cfs).** TVA system; 9 dams.

Hydrologic Significance

• Ohio contributes **60% of Mississippi River flow** at Cairo, IL confluence.
• Tennessee + Cumberland = **~50% of Ohio's flow** — Tennessee Valley Authority controls.
• Navigation: 9-ft channel maintained to Pittsburgh (locks/dams).
• Water quality: Legacy (steel, coal, chemical) + current (ag, urban, CSOs).