The bonytail is the rarest of the endangered, native fish of the Colorado River and is thought to have evolved around 3 to 5 million years ago. Its name describes the fish as an elegant swimmer and member of the chub group of minnows.

Bonytail were once common in portions of the upper and lower Colorado River basins. In the early 1900s, Chuck Mack of Craig, Colorado, called them broomtails, because “…you could get a firm grip on their bony tail.” Mack, and other old-timers, used to catch these fish in the upper Colorado River basin, along with Colorado pikeminnow and razorback sucker.

Recovery efforts for this species are ongoing, with stocking occurring at multiple locations in both the upper and lower Colorado River basins. Threats to the species include streamflow regulation, habitat modification, competition with and predation by non-native species and hybridization.

The humpback chub is a native species of the Colorado River that evolved around 3.5 million years ago and is only found in warm-water canyons of the Colorado River basin. The humpback chub was first described from a fish caught in 1933 near Bright Angel Creek, a tributary of the Colorado River in Grand Canyon, making it one of the last large fish species to be described in North America. The species was protected under the Endangered Species Act in 1973 because large dams and human water use changed the river flow. Actions to conserve the humpback chub include managing river flows, providing passage around dams, and removing non-native predators. Monitoring of humpback chub populations indicates that management actions are benefiting the species. In fact, the Little Colorado River population in Grand Canyon is now estimated at more than 11,000 fish, and the Westwater Canyon population in Utah is estimated to exceed 3,300 fish.