Isa Lake is one of the strangest and most intriguing places in Yellowstone. It's one of only a few lakes and rivers in North America that drains both to the East and to the West. Because of its location directly on the Continental Divide, some water goes to the Pacific Ocean, and some to the Gulf of Mexico. To further complicate matters, the drain on the East side of the lake ends up running West, while the West drain runs to the East. In this image, I'm facing West, taking the picture in the mirror of the sign to the East.
The sign reads: Continental Divide Elevation 8262.