When Lewis and Clark left for their expedition what river did they follow?

Before Lewis met up with Clark, he began the expedition on August 30, 1803 in Pittsburgh PA. Lt. William Clark would offer to join Lewis on the expedition weeks later on October 13, 1803 at Camp Dubois (in present-day Indiana). From there, they sailed down the Ohio River towards St. Louis. William Clark would offer to join Lewis on the expedition weeks later on October 13, 1803 at Camp Dubois (in present-day Indiana). They then named their team the "Corps of Discovery." From there, they sailed down the Ohio River towards St. Louis. Meriwether Lewis had spent the time prior to their departure in St. Louis gathering information from mountain men returning from the west. They then departed St. Louis in May 1804 heading up the Missouri River.