Greg. The Bighorn flows right out of the bottom of a large reservoir--very cold water from the bottom. Even if it is 30C outside the water is still very cold for wet wading.
Dave, did you see any carp in the afterdam or in the river? Did you use some small sowbugs?
Try some smaller flies, like #16, #18 sow bugs and scuds. The good old worm works as well. The fish are big and fat just like their countrymen . There is also some monster carp in the backwaters for more techinical fishing.
They stocked Sundance lake with triploids this year as well. It will be interesting to see what the fish look like in 3,4 and 5 years. The trout and perch were very interested in damsel fly nymphs today.