the poudre in fort collins has a couple of runs that are suitable for that level - filter plant is the first run on the river as you head up the canyon. depending on the level, lower mish is also a nice 3- kind of run, but below 3 feet on the rock, it can turn into an exercise in rock dodging.
Lower mish thru bridges w/o pineview falls is class III @ 2.5 on rock. Upper mish w/o mish falls is class III as well right now. Big Thompson is still running and hasn't reached mank status yet. Run the upper below lake estes to the fishing ramp-bony but fun.