Isa Lake, Wyoming

Most of the water-based attractions in Yellowstone National Park, including Old Faithful, drain into the Atlantic Ocean via tributaries to the Missouri.  One exception is Isa Lake, which sits directly on the Continental Divide. It is located at Craig Pass, where the main road through the park crosses the Continental Divide in the park as well. Historically, with spring runoff, the “lake,” a pond really, grows, and spills over its shores down both sides of the Divide. Though some have called it the only natural lake in the world that drains into two oceans, its status as a natural lake is challenged by the substantial road engineering that has altered its form and its drainage behavior. Apparently, too, the hydrology of the area has changed so that the lake often doesn’t fill up with enough water to drain in either direction.