http://www.zionadventures.com/gear-rentals/

If you click on "Narrows footwear" you can see the canyoneering boots. We went in September and didn't need wet or dry suits. I wore a pair of river shorts (basically swim trunks) and was fine.

This place is also where we got the shuttle.

Oh--although I loved those boots while hiking in the river, I was also very glad that I brought flip-flops so I could take the boots off that evening. That felt really nice, so I would recommend that.

And you definitely want a waterproof bag for your sleeping bag, clothes, and maybe food, because you will probably have to swim at some point, and will at least be hiking in chest deep water in a couple of places.