Carp Edema Virus disease is an emerging disease, especially in koi ponds. While the virus was first described in the 1970s in Japan, it has now reached worldwide distribution through the transport of Japanese koi (Cyprinus rubrofuscus) around the world. When new koi start getting "sleepy" and rest on the bottom of the tank or pond without moving, but will actively swim away when disturbed, one must consider the diagnosis of Koi Sleepy Disease. This is a Poxvirus that can cause significant mortality due to hyperplasia and occlusion of blood capillaries in the gill lamellae. Inflammation and erythema of the skin and fins may also occur. Transmission between koi occurs by viruses passing through the water across the gills and infecting the fish. Diagnosis is possible using PCR tests on gill tissue. While there is no effective antiviral treatment for CEV, mortality can be significantly reduced by increasing the salinity of the water to 0.5%. Recovered fish may be carriers for an undetermined period of time. In this presentation, the clinical signs, diagnostic tests, and treatment methods with be discussed to aid in recognizing and preventing this emerging disease.