Yellowstone Lake at 136 square miles (350 km2) of surface area and 110 miles (180 km) of shoreline, is the largest body of water in Yellowstone National Park and the largest freshwater lake above 7000 feet in North America.

The length of Yellowstone Lake is about 20 miles long and 14 miles wide, and while the average depth of the lake is 139 ft (42 m), its greatest depth is at least 390 ft (120 m). Also, the current surface elevation provides for the existence of seven different islands, including: Frank Island (44.42528, -110.36778), Stevenson Island (44.51528, -110.38444), Peale Island (44.28806, -110.31639), Carrington Island (44.45639, -110.55472), Dot Island (44.45194, -110.40972), Molly Island (44.31361, -110.265) and Pelican Roost Island (44.52222, -110.30556).

In winter, the lake freezes over by early December with ice nearly 3 ft (0.91 m) thick covering the lake except where shallow water covers hot springs. Most years, the lake will remain frozen until late May or early June.

Located within Yellowstone National Park, Yellowstone Lake is a naturally occurring lake which drains northward out of the lake from its only outlet at Fishing Bridge, the Yellowstone River. Because the Yellowstone River does not begin to drop substantially until after arriving at the LeHardy Rapids, some four miles distance downstream of the lake outlet, it is believed that the current lake outlet is the actual northern boundary of Yellowstone Lake.

After stopping in Thermopolis Hot Springs for some hot water, I continue northward to Cody, Wyoming, then west on US 20 which follows the Shoshone River upstream where I stop just past the Hayden Arch bridge at a pull out for a couple photograph of the bridge.