A cutbow (Oncorhynchus clarki x mykiss) is a fertile hybrid between a rainbow trout (Oncorhynchus mykiss) and a cutthroat trout (O. clarki). While cutbow hybrids may occur naturally, most native populations of rainbows and cutthroats were separated by geography or habitat. With human introduction of non-native rainbow trout into cutthroat habitat, cutbow hybridization has become a serious threat for native cutthroat populations due to genetic pollution.