Friends of mine live in Mammoth. They were still skiing about a week ago. I would never wear anything like these to cross a serious river or stream. When I was in NZ, I always wore my boots when crossing rivers; way too dangerous otherwise. Once across, I took them off, dumped out the water, wrung out my socks (wool or Patagonia mix), then put them back on and kept walking. Risking falling in a river with a heavy pack on or getting cut up feet in the boonies is foolish as far as I'm concerned.