In general, species persists only in turbulent, high gradient, canyon-bound reaches of large rivers in the Colorado River Basin. The young prefer shallow, low-velocity nearshore pools in the Little Colorado River, and progressively move to deeper, faster areas with increasing size and age. In the Colorado River in Grand Canyon, young-of-year are found in backwater and other near-shore, slow-velocity sites, with similar ontogenetic tendencies. Adults in the Colorado River in Grand Canyon and in the Upper Basin are associated with large eddy complexes. Humpback chub appear to be more active at night. The population in the Grand Canyon has been previously infested with the parasitic copepod "Lernaea cyprinacea", and Asian tapeworm, "Bothriocephalus acheilognathi". Kaeding and Zimmermann also reported 13 species of bacteria, six protozoans, and the fungus Saprolegnia to infect humpback chub. The historic range of the humpback chub is uncertain, but the distribution was presumably more contiguous than in the present. There were possible populations in and below the Flaming Gorge that were likely destroyed by the poisoning of the Green River associated with the construction of the Flaming Gorge Reservoir. The fish's distribution within the Grand Canyon has contracted since the construction of Glen Canyon Dam. For 2008 the total population of the humpback chub in the Grand Canyon is estimated at 6000 to 10.000. This is a 50-percent increase over the estimation of 2001 and a reversal of the declining trend between 1989 and 2001. It seems that a combination of human-caused and natural events stabilized the population, particularly the experimental flooding of the canyon and the increase in water temperatures due to draught conditions over the last decade. Threats: altered hydrology and cold tailwater releases from reservoirs; Predation by and competition with nonnative fishes; and, parasitism. Management Needs: ameliorate effects of reservoirs; ameliorate effects of nonnative fish and parasite sources in chub waters; monitor status of all populations. Also need to be concerned about genetic isolation of populations by dams. The humpback chub's status as an endangered species has prompted elaborate and expensive programs to restore its numbers, largely by modifying the releases from Glen Canyon Dam, creating artificial floods to replicate historic conditions in the Colorado, and removal of non-native predators, such as rainbow trout. Effective April 20, 1994, seven reaches of the Colorado River System (totaling 379 miles) were designated as Critical Habitat for "Gila cypha".