After being devastated by whirling disease in the 1990s, rainbow trout populations are increasing in most major rivers in the state thanks to a 20-year effort by Colorado Parks and Wildlife aquatic scientists and biologists. The comeback is positive news for anglers who can once again fish for rainbows and brown trout in Colorado’s big rivers and streams. For the past 15 years brown trout have dominated most of the state’s rivers. But since last summer, anglers have reported that they are catching nice size rainbows in the upper Colorado, Rio Grande, upper Gunnison, Poudre, East, Taylor, Arkansas and Yampa rivers and others. The whirling disease problem started in 1986 when a private hatchery unknowingly imported infected rainbow trout from Idaho that were stocked in 40 different waters in Colorado. The disease eventually spread throughout the state and even infected CPW hatcheries which caused more waters to be infected.