Lewis Lake is located in the U. S. state of Wyoming in the southern part of Yellowstone National Park, about 4 miles (6.4 km) southeast of Shoshone Lake, and approximately 10 miles (16 km) southwest of Yellowstone Lake. Lewis Lake and Shoshone Lake are both located a few miles northeast of the Pitchstone Plateau.
The Lewis River is the lake's primary inflow, draining south from Shoshone Lake. The primary outflow of Lewis Lake is also the Lewis River, continuing south to join the Snake River near the southern boundary of Yellowstone National Park. A few small creeks also feed Lewis Lake. There are several hot springs emptying into the lake on its northwestern shore and two more hot springs at the lake's southern end where it empties into the Lewis River. A campground is located on the lake's southeast shore. Yellowstone National Park's South Entrance Road (which is also numbered as U.S. Route 287, U.S. Route 89, and U.S. Route 191), run along the east side of Lewis Lake.
Like the river, Lewis Lake is named for Meriweather Lewis, commander of the Lewis and Clark Expedition.
Lewis Lake Angling
Lewis Lake is a popular brown and lake-trout fishery. The 2,716-acre (10.99 km2) lake is 12 miles (19 km) north of the South Entrance, on the West Thumb–South Entrance Highway. This is the only lake besides Yellowstone Lake that allows motorized watercraft.
This is also the only lake we know of where you can catch brook trout, browns, cutthroats, and lake trout on a dry fly. Most of the angling pressure is from spin fishers, but a few local fly anglers make the lake a regular stop, fishing the drop-off along the southwest shore with sinking lines and leech imitations.
Fishing from a tube or a boat is more reliable than wade fishing the outlet. The best times to fish Lewis Lake are at ice-out in mid-June, warm summer evenings, and late October, when the spawning brown trout become aggressive. Streamers and leeches are effective in the early and late season with caddis the fly of choice on warm summer evenings.