Although the brook stickleback, Culaea inconstans, is not native to Utah, the species has been introduced to several locations in the state. An established population of the brook stickleback is known to occur in the Green River in Uintah County. The brook stickleback has also been introduced to Utah Lake and Willard Bay Reservoir, but it is not known if the species has become established in those areas. The brook stickleback is native to Canada and the northern United States.
Like other sticklebacks, the brook stickleback is small (length of about 2.5 inches) and lacks scales. Males build and guard nests, being extremely aggressive towards any fishes that enter the nesting area. The brook stickleback eats small aquatic animals, mostly invertebrates.