DENVER (AP) – Colorado wildlife managers say rainbow trout are finally recovering in most of the state’s major rivers after they were devastated in the 1990s by an ailment called whirling disease.

Colorado Parks and Wildlife said Tuesday a 15-year effort to crossbreed native trout with a disease-resistant strain from a hatchery in Germany has paid off. Anglers are catching the new strain in the Colorado, Rio Grande, Gunnison, Poudre and Arkansas rivers, among others.

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The disease deforms the spine of young fish, causing them to swim in a whirling pattern. They die shortly after they’re infected.

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Officials say the disease was introduced to Colorado in 1986 when a private hatchery unknowingly bought infected rainbow trout from Idaho. By the mid-1990s, it spread throughout the state, and rainbow trout stopped reproducing naturally.

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