It has two major branches, the Tug Fork and the Levisa Fork. The Big Sandy River and the Tug Fork form the boundary between Kentucky and West Virginia. The Levisa Fork joins the Tug at Louisa, Kentucky. The Big Sandy then flows northward, meeting the Ohio River at Ashland, Kentucky.
From the confluence of the two forks to its mouth at the Ohio River, the Big Sandy River is about 25 miles long.
The Big Sandy River carries commercial shipping, primarily coal mined nearby.