Lewis and Clark’s 1803 journey of exploration of the western part of what would become the United States via the Missouri River to the West Coast often is identified as starting on the Mississippi River near St. Louis. How did Lewis and Clark get to the Mississippi? Lewis started the river journey in Pittsburgh, going down the Ohio and picking up Clark in Louisville. The Ohio River was very different then. Lewis and his crew spent many days dragging their boat over rock because the water was so shallow.