Someone early on posted that they used a rubber soled water shoe, which is what I carry. I've never had to use them for crossing a river yet, but a future planned hike I'm looking at has a couple of crossings in it. I've used them for swimming and kayaking, and they seem to work well.
The one thing I don't like about crocs is that I don't seem to get a good stable footing with them, and with my luck, I'd scrape the skin off the side of my ankle when my heel slips in them. Just the way my foot is built.
There's one thing that I just don't get, which is the recommendation of taking off your hiking boots, remove socks, put hiking boots back on, cross river, remove boots, dump out the water, put back on socks, put back on boots, and away you go. If I'm putting on wet boots over dry socks, those socks are gonna get wet. Why bother to take them off in the first place? Is it to reduce the amount of wetness in the socks? I've just never heard of this before reading this post, and I'm curious as to what I'm missing.