Isa Lake (in the visual explanation) 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. Isa Lake is believed to be the only natural lake in the world which drains to two different oceans. The east side of the lake drains by way of the Lewis River to the Pacific Ocean and the west side of the lake drains by way of the Firehole River to the Atlantic Ocean. This is the opposite of what one would expect since the Atlantic Ocean is east of the lake and the Pacific Ocean is to the west.

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