Crocs made a river shoe a few years back. Std Crock with a neoprene ankle and a cinch tie in back. Gravel gets in, but washes back out of the holes. Pretty grippy. Stayed tight on foot, even wore them over stocking foot waders in a pinch. But they work, drain when you pick them up out of the water. I am going to miss them when I wear them out. They were perfect for wet wading and reside in the back of the Sequoia year round.