FROM WIKI:
Ten people have died in the last decade by entering the water above Vernal Falls, including the Silver Apron and Emerald Pool. In fact, one person died in May 2007 after hopping from rock to rock around the falls. Strong undercurrents exist that may not be visible from the surface. Clearly, swimming above a waterfall can carry with it a great deal of risk, and it is against the park rules; nevertheless, tourists have been known to be swept over the Yosemite Valley’s waterfalls to their deaths.[6]
Gee, d'ya think!