The only trout native to the park were the greenback cutthroat and the Colorado River cutthroat. Discuss them with other fishers in GORP's Rocky Mountain forum . The National Park Service stocked non-native Yellowstone cutthroat trout as late as 1968. Removing exotic or non-native fish and restocking with native greenback cutthroat and Colorado River cutthroat trout are returning park waters to a original condition. Populations of at least four species of trout exist in the park brown brook, rainbow, and cutthroat.
Some suckers also inhabit the streams and lakes.
Only 42 of the 156 lakes in the park have reproducing populations of fish. Cold water temperatures and lack of spawning habitat prevent reproduction in other high altitude lakes. Supplemental stocking is done only to restore native species to altered waters. Successful fishing at high altitudes is spotty, even from waters known to contain fish. The possession limit has been held to a minimum, resulting in an increasing population of cutthroat, brown, and rainbow trout.