A rare trout species native to Colorado is making a comeback with a surprising strategy called "Trojan trout." 

What's happening?

According to Denver Water, efforts to restore the green lineage cutthroat trout — a rare subspecies of Colorado River cutthroat — are showing signs of success. 

These fish have been in decline since the mid-1800s because of human activities like mining and logging. Invasive brook trout were also outcompeting native cutthroats. At one point, there were fewer than 40 of them counted in streams.

But a collaborative project between the water company, Colorado Parks and Wildlife, and the U.S. Forest Service has more than tripled those numbers. Recent counts show more than 1,400 cutthroats in the creeks, thanks to years of electrofishing (a method that stuns and removes the invasive fish) and dam upgrades designed to block brook trout from swimming upstream. 

A new method being tried for the first time in Colorado is also helping — introducing "Trojan trout," or fish that only produce male offspring. Over time, biologists say this technique could naturally eliminate brook trout without harming other species.

Why is restoring threatened species important?

Restoring native fish like the cutthroat trout helps protect the balance of entire ecosystems. Unlike the invasive brook trout, the native green lineage cutthroat trout evolved with and has an important role in the local ecosystem. 

Losing them could throw the food chain out of balance, impacting other species, water quality, and local communities — all because nature is a web of interconnectivity. The project also shows how human-made problems can be solved through collaborative, innovative efforts.

What's being done to protect threatened species?

In Colorado, conservationists will continue to restore the native cutthroats with electrofishing, releasing "Trojan trout," and monitoring the population. On a broader scale, governments, conservation groups, and the public are working together to restore threatened species like bison, seabirds near Madagascar, and Australia's Gilbert's potoroo, a marsupial that was thought to be extinct.

Individuals can help by educating themselves about critical climate issues, supporting clean water policies, and following Leave No Trace principles when enjoying the great outdoors.

"We're excited to be able to help out with this effort to protect the cutthroat trout," said Jason Marks, an environmental planner at Denver Water. "This project is a great example of how multiple agencies can work together and we're all looking forward to more projects down the road."

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