<P> The Tall Stacks festival celebrates the riverboats of Cincinnati, Ohio, every three or four years . </P> <P> The Ohio River is formed by the confluence of the Allegheny and Monongahela rivers at Point State Park in Pittsburgh, Pennsylvania . From there, it flows northwest through Allegheny and Beaver counties, before making an abrupt turn to the south - southwest at the West Virginia--Ohio--Pennsylvania triple - state line (near East Liverpool, Ohio; Chester, West Virginia; and Midland, Pennsylvania). From there, it forms the border between West Virginia and Ohio, upstream of Wheeling, West Virginia . </P> <P> The river then follows a roughly southwest and then west - northwest course until Cincinnati, before bending to a west - southwest course for most of its length . The course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River near the city of Cairo, Illinois . </P> <P> Major tributaries of the river, indicated by the location of the mouths, include: </P>

What body of water forms the northern boundary of kentucky
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