Re: April or May wading opportunities in the Rockies
The early Spring or late Fall are great times to fish The Green River below Flaming Gorge, after that you can head west a couple hours and hit The Provo River around Heber City and then head North to Idaho and fish the Box Canyon and lower Henry's Fork around Ashton and St Anthony, this area always fishes well in the early season and is very accessible by wading.
Good luck and have fun wherever you go.
*Comments posted above are only my opinion. I may be right....eh, I'm probably wrong. Take 'em for what they're worth.*