[1] The Ohio River forms its southern border, though nearly all of the river itself belongs to Kentucky and West Virginia.
The rivers in the northern part of the state drain into the northern Atlantic Ocean via Lake Erie and the St. Lawrence River, and the rivers in the southern part of the state drain into the Gulf of Mexico via the Ohio River and then the Mississippi.
The worst weather disaster in Ohio history occurred along the Great Miami River in 1913.
Known as the Great Dayton Flood, the entire Miami River watershed flooded, including the downtown business district of Dayton.
As a result, the Miami Conservancy District was created as the first major flood plain engineering project in Ohio and the United States.