Bacterial cold water disease (BCWD) is a bacterial disease of salmonid fish. It is caused by Flavobacterium psychrophilum (previously classified in the genus Cytophaga), a gram-negative rod-shaped bacterium of the family Flavobacteriaceae. The disease typically occurs at temperatures below 13°C, and it can be seen in any area with water temperatures consistently below 15°C. Salmon are the most commonly affected species. This disease is not zoonotic.