A native greenback cutthroat trout collected during a population survey at Herman Gulch.

Courtesy Colorado Parks & Wildlife

State wildlife officials say Colorado's state fish— once thought to be extinct — is making a comeback.

It's been a tough road for saving the native greenback cutthroat trout. At one point, biologists were protecting and stocking the wrong trout, but they got that sorted out. Now, healthy numbers of the fish are surviving after thousands were stocked in recent years along a stretch of Clear Creek near the Eisenhower Tunnel.

Aquatic biologist Boyd Wright and his team have been stocking greenbacks into the Clear Creek headwaters four miles above Interstate 70 near the tunnel for the past three years.

Following a September population survey, Wright said it had, "been a long road with lots of hard work by some really good and passionate people." 

Parks and Wildlife say they are seeing more than 400 of the trout in each mile of river. By next year, some of the stocked fish will be old enough to reproduce. 

Officials hope they will now be able to sustain their own population.

Wright says scientists will be able to tell whether their conservation efforts are really working by 2020.

The greenback cutthroat trout isn't the only threatened Colorado fish to be pulled back from the brink of extinction. The razorback sucker, humpback chub and San Juan cutthroat trout populations have also been recovered in the state's rivers.