To Reverse The Disappearance Of Native Fish, Northern Colorado Is Turning To Fish Ladders

Mar 21, 2018

Standing at the edge of the Cache La Poudre River in Fort Collins, Boyd Wright adjusted his sunglasses against the bright sunlight. He pointed to the Fossil Creek ditch, a diversion structure dividing the waterway.

His focus was a narrow concrete chute jutting out downstream from the structure's north side. Cool water rippled down the chute like a water slide, forming a small set of rapids.

Wright, a fish biologist with Colorado Parks and Wildlife, explained how this “fish ladder” – officially Larimer County’s first – could be the last hope for dozens of northern Colorado’s native fish species.

“In terms of diversity, there’s much fewer [fish] species than there were here historically,” he said. “I don’t have a crystal ball, but that said  — we are at risk, certainly, of losing some of these species all together from the state of Colorado.”

Over the last decade, Great Plains fishes like the common shiner and the central stoneroller have disappeared from the Poudre River and other northern Colorado waterways, Wright said.

An orangespotted sunfish, one of about a dozen Great Plains fish seeing a population decline in northern Colorado. Adults usually grow to about 4 inches in length, the exact size for Fort Collins’ new fish ladder.
Credit Jonathan Wardell, Courtesy Colorado State University

One of the main causes is man-made diversion structures. While necessary for the agriculture industry and flood control, Wright and other researchers believe the structures confine fish to shorter stretches of habitat.  

Even small minnows like the red shiner and orangespotted sunfish, which are still found in northern Colorado, need at least 30 miles of uninterrupted habitat to migrate and spawn.  

Along the Poudre in Larimer County, the average stretch is less than two miles, according to Fort Collins’ Natural Areas Department.

The result: An estimated 82 percent of Great Plains fish species are in decline in northern Colorado. Other factors contributing to population decline, he added, could be low river flow or disease.

“For a state that prides itself for being tuned in with its wildlife and having an emphasis on nature, I don’t think that’s anything citizens in Colorado really want to see,” Wright said.

The best solution scientists have is the fish ladder.

Bolted down rock climbing holds are used to simulate rocks along a 40-foot-long fiberglass “stream” inside Colorado State University’s Fish Physiological Ecology Laboratory
Credit Matt Bloom/KUNC

Designing the right ladders

In an unmarked building on Colorado State University’s foothills campus, professor Chris Myrick is about to turn on his new favorite toy.

It’s a 40-foot-long fiberglass slide, used to simulate real-world stream conditions. Rock climbing holds bolted along the bottom simulate underwater rocks.

Fish ladders for larger fish, like salmon, have been around for hundreds of years, Myrick said. But ladders for weaker fish weren’t around until his team began running tests with the slide at CSU’s Fish Physiological Ecology Laboratory.

Myrick calls it “Tyler’s massively awesome flume.” It’s named after his graduate student Tyler Swarr, who built the structure by hand about two years ago.  

“It’s going to make a really cool wooshing noise as the water comes up through that blue tank,” Myrick said, flipping the switch.

Immediately, water bubbled up and poured over the edge of a tank suspended almost two stories in the air, spilling down the slide. The sound of a roaring river filled the room.

Colorado State Professor Chris Myrick, who heads the school’s Fish Physiological Ecology Laboratory, holds a rubber fish used in studies. Behind him, a 40-foot-long simulated stream bottom is used to test out fish ladder designs that are now being built along the Cache La Poudre River in Larimer County.
Credit Matt Bloom / KUNC

Since the flume’s construction, researchers at Colorado State University have conducted several studies to better understand how weaker-swimming Great Plains species can benefit from fish ladders. Myrick has found that, for fish shorter than 4 inches, the sweet spot is around a 5 percent grade.

He hopes his team’s new findings can eventually be used far beyond northern Colorado’s waterways to help the “little guys.”

“[Our] idea was that we could use [the design] to figure out how steep you could go with one of these rock ramp fish ladders for any of the small fish you find on the eastern plains – not just in Colorado but clear up into Montana and out toward Kansas and Nebraska as well,” he said.

According to Colorado Parks and Wildlife, steeper fish ladders for cutthroat trout have been installed in other parts of Colorado, including the Western Slope and parts of the Colorado River as well as in Colorado Springs.

Plans to build more

The Fossil Creek ladder in Fort Collins – finished in February – is the only working ladder in Larimer County.

Fundraising is underway for several more projects, which can cost anywhere from $10,000 to more than $100,000 each to build and maintain, according to Jennifer Shanahan, a watershed planner with Fort Collins’ Natural Areas Department.

“Right now, the city and Colorado Parks and Wildlife are working on collaborations,” she said. “There are several, but agreements aren’t all in place.”

One confirmed project is the removal of the Coy diversion in downtown Fort Collins happening later this year.

A Colorado Parks and Wildlife map marks the location of man-made diversion structures along the Poudre river between Larimer and Weld counties. Credit: Colorado Parks and Wildlife.
Credit Colorado Parks and Wildlife.

Most of the river’s man-made structures are owned by 22 private irrigation companies based along the Front Range, many with water rights dating back more than 100 years.

Shanahan said working with them to build the ladders is a slow part of the process, but critical one.

“Their rights and assets come first when we start designing these structures,” she said. “We need to respect their property rights.”

Through meetings, the City of Fort Collins, Colorado Parks and Wildlife and CSU are hoping to strike new partnerships with the companies to help finance the construction of more fish ladders along the Poudre.

“There are also some opportunities for these projects to create side benefits for the structures,” she said. “Updating, modernizing or improving some aspects.”

Tad Moen, general manager of North Poudre Irrigation, which owns the Fossil Creek ditch, said joining the fish ladder effort at first took some convincing and brainstorming with staff at the Natural Areas Department.

“Growing up in this area you always thought the Poudre was flourished with fish and it was a never ending deal,” he said. “But seeing the actual numbers and how everything was affected by happenings on the Poudre  — it was a surprise.”

Moen said he now strongly supports fish ladders because they contribute to the overall health of the river’s ecosystem. North Poudre Irrigation is also planning to build fish ladders on its two other diversion structures upstream over the next decade, he added.

“[Now] we don’t even notice [the fish ladder] is there,” he said. “It doesn’t affect us in the slightest bit.”

North Poudre Irrigation is the only company to publicly commit to investing in fish ladder construction, according to Shanahan. Meetings are underway, she said, and more could come on board in the next few months.

Shanahan could not comment on the current number of public-private agreements being finalized.

Other municipalities along the Poudre River have also taken note of Fort Collins’ efforts to expand fish habitat but are further behind in the construction process.

Jennifer Shanahan, watershed planner with the City of Fort Collins’ Natural Areas Department.
Credit Matt Bloom/KUNC

In Windsor, the town’s Parks, Recreation and Culture Department has commissioned preliminary designs for fish ladders along the Poudre, but has no definitive construction schedule, according to the agency.

A spokeswoman with Greeley’s Forestry, Natural Areas and Trails Department confirmed the city has considered ladders to help expand fish habitat along the Poudre. But, so far, no further action has been taken.  

Shanahan said Fort Collins’ Natural Areas Department also recently received a $100,000 grant from the Colorado Water Conservation Board. The grant will fund a study of small minnow movement through the new Fossil Creek ladder — as well as studies of future ladders.  

“We’re trying to understand where [the fish] are trying to move and how often they’re successful in bypassing the fish structure that’s already installed,” she said. “It’s an exciting study to help us understand the background issue better.”

With help from CSU, the study will take place over the next three years.

“Overall our goal is to support river health as a whole,” she said. “[These fish] are one of the most vulnerable aspects of this system and that’s why we’re making it our focus.”