Yosemite
Emerald Pool is a small, shallow lake located immediately above Vernal Fall in Yosemite National Park. It is named for its deep green color, which is caused by algae living on the rocks at the bottom of the pool. In the summertime during diminished water flow, the Silver Apron (a smooth granite slope over which the Merced River flows into the Emerald Pool) is frequently (albeit illegally) used by hikers as a water slide. Swimming or wading in the Emerald Pool or entering the Silver Apron is prohibited by the National Park Service as waders or swimmers have been swept over Vernal Fall. This prohibition is clearly marked with signs.
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