The parasitic disease probably originated in Europe, where native brown trout have developed a natural resistance to the parasite through co-evolution. But these fish can still carry and transmit the spore.

Impact On Fishing
Overall, whirling disease has had little impact on recreational fishing in Colorado. Mature stocks of healthy fish continue to thrive in most waters, and whirling disease has not been identified in any wild populations of native Colorado cutthroat trout. The full effects of whirling disease in the wild probably won’t be apparent for several years. But the parasite’s presence in state hatcheries has required that stocking schedules be modified. Meanwhile, the Division of Wildlife is working to stop the spread of the disease and raise disease-free fish to release into the wild.

Anglers can help prevent the spread of whirling disease in Colorado by following these basic guidelines:

• Remember that the tubifex worm can hold the whirling disease parasite. Thoroughly wash off any mud from vehicles, boats, trailers, anchors, axles, waders, boots, fishing equipment and anything that can hold the spores or mud-dwelling worms.
• The parasite can persist in water. Drain boats, equipment, coolers, live bait wells and any holder of water. Make sure you don’t inadvertently help spread whirling disease by cleaning all equipment after use in lakes or streams.
• Don’t transport any fish from one body of water to another, which can help spread whirling disease. It is unlawful in Colorado to move and stock live fish without a special license.
• Don’t dispose of fish entrails or other by-products into any body of water.
  Never transport aquatic plants. Make sure boats, engine props, anchors, trailers and wheels are cleared of weeds after every use.

More Information on Whirling Disease