North of Moab, the Colorado River is popular with fishermen, but can be a challenge for fly fishing due to its murky visibility. It's actually really popular for it's catfish population, though there are some bass and sunfish.
There is excellent fishing access on the Colorado River along SR128. There are turnouts, parking areas and primative campgrounds.
Overall, Colorado River is the 8th most popular fly fishing river of all 12 fly fishing spots in Utah.