Yellowstone Lake is 136 square miles with 110 miles shoreline and goes 387 ft deep. It's the largest high altitude freshwater lake in the North America and the second largest in the world. There are numerous active geothermal features under the lake including a recently discovered bulge that is 2000 ft long and 100 ft tall in an area rich with faults, hot springs and craters. Also there are two volcanic vents rising again on the lake floor (resurgent domes similar to what's happening on Mt. St. Helens in WA state).