On the west coast of Canada on Vancouver Island in British Columbia, there is a species of freshwater parasitic lamprey found nowhere else in the world, the Cowichan Lake lamprey. This fish spends its whole life in Cowichan and Mesachie lakes. This water system is managed by a weir on Cowichan Lake. The dam holds water in Cowichan Lake so that it can be let out into the Cowichan River when the water supply in the river is low. People use the water from the river for drinking, sewage treatment, businesses, and recreation. It is also important to have water in Cowichan River to support all aquatic plant and animal species that live there.
Compared to some other lamprey species which grow as long as 120 cm long, Cowichan Lake lamprey are small, a total length of about 27 cm. Like all lamprey species, Cowichan Lake lamprey spend most of its life as an ammocoete, but then undergoes metamorphosis. During metamorphosis, an ammocoete changes into an adult with functional eyes, mouth, and digestive system. After metamorphosis, the Cowichan Lake lamprey is a parasitic adult and cutthroat trout are one of their favorite foods.

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