Whirling disease is a parasitic infection of trout and salmon that can cause the infected fish to whirl or spin when startled or while feeding, hence the name whirling disease.
Impacts:
Whirling disease can cause very high mortality rates amongst young fish; as high as 90% in some situations. However, anglers should be aware that this evidence is rarely visible in wild populations. Fish that are severely infected will die as juveniles, and the impact of a severe WD infection will manifest itself in declining populations and is verified only through laboratory testing.

The spread of whirling disease:
One of the major means by which whirling disease is spread is the movement of infected fish. Such movement can occur in wild populations and in association with fish culture and stocking activities. Once established in a natural system, the parasite can spread as infected fish move up or down stream and by passive downstream drift with the current. The parasites can be carried by predators that eat infected fish and then shed spores in their feces. They may also be transferred through mud on waders and boots or on boats, or other items moved between infected and uninfected waters. Whirling disease could also be spread through shipments of fish food infected with the parasite (in fact, it is believed that whirling disease first came to the United States in frozen food fish from Europe).

What TU is doing:
When TU first issued "Whirling Disease in the United States" in 1999, the report included a series of priority research recommendations. Researchers from state and federal agencies and academic institutions have tackled many of the priorities identified in the report; Much of the current research on whirling disease has been funded by the US Fish and Wildlife Service. Unfortunately, funds were cut in 2008. Trout Unlimited has since provided critical research in the area of whirling disease resistant trout.