DURANGO, Colo. (AP) — While firefighting crews were in the throes of battling the 416 Fire as it rapidly spread through the San Juan National Forest north of Durango in June 2018, an unlikely rescue mission was being hatched.

Jim White, an aquatic biologist for Colorado Parks and Wildlife, said plans had to move fast as the blaze started inching toward prime habitat for a rare lineage of cutthroat trout that lives in the remote side streams of Hermosa Creek.

Colorado Parks and Wildlife knew what was at risk: the potential loss of a native fish that had survived in isolation, against the odds,...