Isa Lake is located in Yellowstone National Park, in the U.S. state of Wyoming. The lake straddles the continental divide at Craig Pass and was first discovered in 1891 by Hiram M. Chittenden, who was exploring the best routes for a road to connect Old Faithful and West Thumb geyser basins. Chittenden named the lake after Miss Isabel Jelke, from Cincinnati, though it is not clear why.