Our trip was in late August. That was a pretty good time for it, as the weather was fine (mostly warm to somewhat hot, and sunny), and the flow was low enough to be reasonable for canoes. I don't think I would want to take a canoe down that stretch of river in the late spring, with the typical flows at that time. This year, with the above normal snowpack in Utah (although apparently not quite so much in southern Wyoming), I think the flows are going to be pretty large in May. That might be a lot of fun in a packraft, though, and if Cataract Canyon is doable, then certainly this should be.