The search and rescue team put on a demonstration to educate the public about how dangerous the river is.
It's flowing at full capacity right now, and rangers say even areas that appear calm on the surface can have very powerful currents.
The snowmelt also keeps the water very cold all year round. Even on a ninety degree day, the water is typically around fifty degrees.
Yosemite swift water trainer Moose Mutlow said, "Out of 250 rescues a year that Yosemite search and rescue run, there's gonna be 10-12 water events, unfortunately last year most of our water events were actually recoveries, people who drowned."
Last summer, three young hikers from the Modesto area died after being swept over Vernal Fall.
Witnesses said they had walked out into the seemingly calm water above the fall to take pictures.