In the headwaters of the Colorado River, a rare trout species is making a comeback
Hidden in the hills below the Continental Divide in a remote section of Grand County, Colorado, are several small streams that are home to a rare species of fish.
The fish on the west side of Jones Pass area are green lineage cutthroat trout. They’ve been in decline since the late 1800s and have been identified as a “sensitive species” in Colorado by the U.S. Forest Service.
But thanks to efforts by the U.S. Forest Service and Colorado Parks and Wildlife, the cutthroats are making a comeback and also getting additional help from Denver Water.
Over the years, Denver Water has worked with state, federal and community partners to improve wildlife habitat in Grand County streams where the utility collects water for 1.5 million people in the metro area.
Denver Water’s past projects on the Fraser Flats section of the Fraser River, Vasquez Creek and Cabin Creek improved aquatic habitat. Two new projects on Bobtail and Steelman creeks will help protect the cutthroats from nonnative brook trout.
Native fish in troubled waters
The green lineage cutthroat trout, a subspecies of Colorado River cutthroat trout, is native to the Bobtail, McQueary and Steelman creeks in Grand County, about 15 miles southwest of Winter Park. The creeks flow into the Williams Fork River, which flows into the Colorado River.
The cutthroats found in these high-mountain, remote creeks are considered to be the highest-value, most genetically pure native cutthroat populations in the headwaters of the Colorado River.
However, their numbers have fallen since the 1860s when settlers started moving to Colorado.
Human activities like mining, logging and water diversions impacted the fish populations. And they faced an even greater threat from brook trout, which are not native to Colorado.
Brook trout are common in the eastern U.S. and Canada. They were introduced in Colorado during the days of westward expansion in the late 1800s and early 1900s. They were used as an additional food source for the new settlers and for recreational fishing.
“The problem is in the rare areas of the state that have native cutthroat trout, they can’t compete with the brook trout,” said Jon Ewert, an aquatic biologist with Colorado Parks and Wildlife. “Over time, if nothing is done, it’s just a matter of time before the cutthroats will disappear from streams that have brook trout in them.”
Brook trout spawn in the fall and their fry — baby fish — emerge in the spring. Cutthroat trout spawn in the spring, so their fry emerge later in the year.
This means the brook trout are bigger and more established when the baby cutthroats emerge. The bigger brook trout not only outcompete the cutthroats for food, they even prey on the young cutthroats.
In 2010, Colorado Parks and Wildlife’s fish counts found fewer than 40 green lineage cutthroats in all of Bobtail Creek and similar numbers in Steelman Creek, an alarming statistic that Ewert said required immediate action to save the cutthroat populations.
Taking action
The Forest Service manages millions of acres of national forests, including the habitat of these rare trout populations. The agency has been monitoring the cutthroats, in collaboration with the state parks and wildlife department, across public lands managed by the Forest Service in Grand County.
“As a sensitive species in our region, we manage the habitat where the cutthroats live to keep them viable and prevent their decline, so they don’t end up on the federal Endangered Species list,” said Eric Freels, Sulphur District Ranger with the Forest Service in Grand County.
“Here in the Jones Pass area, the brook trout have aggressively moved into the native cutthroat trout habitat.”
In 2011, Colorado Parks and Wildlife and the Forest Service teamed up to start removing brook trout from Bobtail and Steelman creeks through electrofishing.
“Electrofishing is when we walk up and down a stream and put electric current into the water that stuns the fish so we can catch them,” Ewert said.
Parks and Wildlife workers measure, weigh and count the cutthroats before putting them back in the water, while the brook trout are removed from the stream.
Parks and Wildlife has done electrofishing most years since 2010, and the removal efforts have paid off. Cutthroats now outnumber brook trout in the two streams by about 5 to 1.
Denver Water’s role
Denver Water collects water from Bobtail and Steelman creeks. The water provider also works with the Forest Service on habitat issues.
“In this area, Denver Water is making two infrastructure changes so aquatic biologists can essentially split the creeks into upper and lower sections and protect the cutthroat habitat in the upper section,” said Jason Marks, an environmental planner at Denver Water.
Denver Water has diversion dams on both creeks. While not their primary function, the dams also act as barriers to fish movement.
But during the spring runoff, when the water in the creeks is higher, brook trout are capable of jumping over the top of the dams or they can swim through the dams’ sluice gates when they are open.
To help prevent the brook trout from swimming upstream into the native cutthroats’ habitat, Denver Water crews replaced two existing culverts on its service road downstream of its diversion dam on Bobtail Creek.
The old culverts were level with the stream on both ends, which allowed fish to swim up the creek to the diversion dam and sometimes get past the dam in certain situations.
In the fall of 2024, Denver Water removed the old culverts and replaced them with three pipes that are 55 feet long and positioned to have a 4-foot drop between the end of the pipe and the water below on the downstream side.
The longer pipe and the 4-foot drop are intended to make it virtually impossible for brook trout to swim upstream into the cutthroat habitat.
Later this year, Denver Water will begin work on a second fish barrier on nearby Steelman Creek.
That project calls for modifying the sluice channel on the Steelman Creek diversion dam by adding a 60-foot-long pipe with a 4-foot drop between the pipe and the downstream side of the creek.
“The new Bobtail Creek culvert and modification to the Steelman Dam sluice channel will be additional barriers for the brook trout,” said Travis Bray, interagency project manager at Denver Water. “We’re hoping the fish won’t be able to jump up into the pipes and even if they can, they likely won’t be able to swim up the long pipes.”
Bray said Denver Water is always working with partner agencies to find creative ways to improve stream habitat.
“This project was identified as part of an agreement between Denver Water and the Forest Service to address issues on the West Slope related to our historic water diversions,” Bray said.
“It's really rooted in cooperation and protecting the environment in locations where Denver Water has operational facilities.”
Releasing “Trojan trout”
Along with removing brook trout and modifying infrastructure on the streams, the state’s aquatic biologists are also trying another method to protect the cutthroat trout in Bobtail and Steelman creeks.
In September 2024, Ewert led a group of workers and volunteers into the wilderness to release 240 “Trojan trout” into each stream.
According to Ewert, the Trojan male or “YY trout” — are male fish that are incapable of producing female offspring. So, over time, the brook trout will simply disappear as there are no female fish in the stream to reproduce.
The fish-management technique has been used by other states such as Idaho, but this is the first time it’s been tried in Colorado. You can learn more about the innovative approach in this article from Colorado Outdoors magazine.
Looking ahead
The future of the green lineage cutthroat trout is looking bright according to Ewert.
In 2011, CPW found just 123 cutthroats in Bobtail and Steelman creeks. In 2024, the number of cutthroats they found grew to 1,425. That increase was achieved solely through the use of electrofishing to selectively remove the nonnative brook trout.
“It really does take partnerships with agencies like Denver Water to protect the native cutthroat trout in these streams,” Freels said. “It takes many years of planning and effort. We come together, we work collaboratively, we bring up issues, and we work through them as a team.”
Colorado Parks and Wildlife will continue removing brook trout through electrofishing as well as stocking the streams with more Trojan trout for several years. Aquatic biologists will continue monitoring the number of brook and cutthroat trout with the added benefit of Denver Water’s fish barriers helping out.
“We’re excited to be able to help out with this effort to protect the cutthroat trout,” Marks said. “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.”
