Yosemite
Emerald Pool is a small, shallow lake, with an area of less than one acre. It is located about 80 meters 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 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 since waders or swimmers have been swept over Vernal Fall and killed. This prohibition is clearly marked with signs.