The Ohio River forms the natural northern border of Kentucky, separating it from the states of Ohio, Indiana, and Illinois. The largest Kentucky city on the river is Louisville. Other significant Ohio River towns in Kentucky are Paducah, Owensboro, Covington (across the river from Cincinnati), Maysville, and Ashland. Just upriver from Ashland is the confluence of the Ohio and the Big Sandy River, which marks the border between Kentucky and West Virginia.