Yosemite National Park rangers are searching for a young woman who fell into the Merced River below the Vernal Fall footbridge.

Rivers can be dangerous any time of year, but those in Yosemite flow fastest and most powerful in spring when they're flush with snowmelt. As the Merced plunges into the Yosemite Valley over Nevada Fall and then Vernal Fall, it is transformed from a somewhat placid stream into a tumultuous cataract.

Yosemite officials say Katrin Lehmann, 31, fell into the river below the footbridge about 3:30 p.m. on Monday.