Ohio River 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 at the city of Cairo, Illinois. Where the Ohio joins the Mississippi is the lowest elevation in the state of Illinois, at . The Ohio River, which flows westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi. Measured by long-term mean discharge in cubic feet per second and cubic meters per second,
Muddy River (Washington) Muddy River Picnic Site, next to the river and to Forest Road 25 in the Gifford Pinchot National Forest. Trails cross the river on its upper reaches. Muddy River originates at about the level on the southeast side of Mount St. Helens in the Cascade Range. The river source is within Mount St. Helens National Volcanic Monument and Gifford Pinchot National Forest. Shoestring Glacier is to the right and East Dome is to the left. Flowing southeast down steep slopes, the river curves sharply to the northeast just beyond the level of the volcano. Here the river crosses Forest Road