The rainbow trout, Oncorhynchus mykiss, is an extremely popular sport fish with Utah anglers. Although the species is native to western North America, it is not native to Utah. It has been introduced, however, to cold and cool waters throughout the state. Because the species is so popular with anglers, and because most Utah rainbow trout do not reproduce in the wild, the Utah Division of Wildlife Resources (UDWR) stocks millions of rainbow trout into Utah waters each year. The UDWR has also stocked an albino form of the rainbow trout into many Utah waters.

Rainbow trout eat primarily invertebrates, including insects, worms, zooplankton, and insect larvae. Some larger rainbows become piscivorous (they eat fish). The species spawns in streams over gravel substrate during the spring. Eggs hatch in about one month, and fry emerge from the gravel about two to three weeks after hatching. In areas where rainbow trout and cutthroat trout co-exist, similarities in spawning time and location often lead to the production of rainbow - cutthroat hybrids. In fact, loss of genetic purity through hybridization with rainbow trout is one of the major threats to Utah's native cutthroat trout.