1. The Missouri River: This was the primary waterway that Lewis and Clark traveled along for a majority of their journey. They started their expedition from Camp Wood near St. Louis, Missouri, and ascended the Missouri River all the way to its headwaters in present-day Montana.
2. The Yellowstone River: Lewis and Clark encountered the Yellowstone River while exploring the upper Missouri River Basin. The Yellowstone River joins the Missouri River in present-day North Dakota.
3. The Snake River: Lewis and Clark encountered the Snake River during their overland journey through the Bitterroot Mountains. The Snake River is a major tributary of the Columbia River in the Northwestern United States.
4. The Columbia River: The Columbia River played a crucial role in Lewis and Clark's exploration of the Pacific Northwest. They traveled down the Columbia River from the interior region to reach the Pacific Ocean.
5. The Clearwater River: While exploring the Columbia River Basin, Lewis and Clark also encountered the Clearwater River, which joins the Snake River in present-day Idaho.
6. The Willamette River: During their time in the Pacific Northwest, Lewis and Clark also explored the Willamette River, which flows through the fertile Willamette Valley in present-day Oregon.
These rivers were vital navigational routes that facilitated Lewis and Clark's exploration of the vast and uncharted territories of the American West.