Dean M. Chriss
Yellowstone Lake and Clouds, Yellowstone National Park, Wyoming

Yellowstone Lake and Clouds

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A volcanic rock formation echoes distant mountains across Yellowstone Lake under an unsettled sky. Yellowstone Lake is the largest natural freshwater lake in the United States above 7,000 feet, and is one of the largest such lakes in the world. During late summer Yellowstone Lake becomes thermally stratified. The topmost layer rarely exceeds 66°F, and the lower layers are much colder, so swimming is not recommended. The lake supports the largest population of wild cutthroat trout in the world, but illegally introduced lake trout now threaten their existence. This situation in turn threatens other species including the grizzly bear. Cutthroat trout move up tributary streams to spawn, and when they do many become food for bears and other mammals. Lake trout stay in the lake to spawn, so as they replace the cutthroat trout these mammals lose a critical food source.