GRAND JUNCTION, Colo. — In a development that could further strain Colorado’s aquatic ecosystems, Colorado Parks and Wildlife (CPW) has confirmed the presence of an invasive and ecologically disruptive species—the rusty crayfish—in the West Fork Little Thompson River.
The May 2 announcement marks the first documented sighting of the species in CPW’s Northeast Region, and only the second time it has been found east of the Continental Divide.
A Threat Below the Surface
The rusty crayfish, native to the Ohio River Basin, is larger and more aggressive than Colorado’s native crayfish species. That aggression poses a problem.
“Rusty crayfish are much more aggressive than our native crayfish species and are not an ideal food source for our sportfish,” said Robert Walters, CPW’s Invasive Species Program Manager.
“They also eat aquatic vegetation, which native fish rely on for spawning, cover, and food.”
The species competes fiercely with native crayfish and fish for resources and habitat. Its feeding behavior—rooting up aquatic vegetation and disrupting sediment—can significantly degrade spawning grounds, reduce cover for fish, and alter nutrient dynamics in rivers.
Public Sighting Sparks Rapid Response
The initial report of the invasive species didn’t come from a scientist—it came from a citizen scientist using a crowdsourced app.
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April 7: A member of the public uploaded a sighting of the crayfish on iNaturalist, a popular app for identifying flora and fauna.
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April 8: CPW’s Aquatic Nuisance Species (ANS) Sampling and Monitoring Team launched a follow-up survey, confirming the presence of the rusty crayfish.
This quick response showcases the importance of community reporting in environmental monitoring, especially as invasive species continue to spread due to water transport, bait release, and shifting habitats.
What Makes Rusty Crayfish So Destructive?
| Trait | Impact on Ecosystem |
|---|---|
| Aggressive behavior | Displaces native crayfish and fish |
| Herbivorous diet | Destroys aquatic vegetation vital for spawning |
| Rapid reproduction | Can dominate ecosystems within seasons |
| Unpalatable to sportfish | Disrupts food chains |
Rusty crayfish are identifiable by their rust-colored spots on either side of the abdomen and dark rings near the tips of their claws. Males can grow up to five inches, and the species is adaptable—able to survive in still or fast-moving waters.
A Growing Problem in Colorado
This latest discovery brings the total to six confirmed water bodies in Colorado where the rusty crayfish has taken hold. Until recently, their spread had been largely contained west of the Divide.
CPW has not released the full list of affected locations, but the agency has emphasized the need for the public to:
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Clean gear thoroughly after water recreation
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Never release bait or non-native species
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Report sightings via apps or directly to CPW
CPW is considering further monitoring and mitigation strategies, including electrofishing, trapping, and public outreach, to try and prevent the species from spreading into connected water systems.
The discovery underscores how fragile Colorado’s waterways remain, especially under the pressures of invasive species, climate stress, and increased recreation. As the state moves into summer—a peak season for fishing, kayaking, and camping—officials are ramping up efforts to contain what they fear could become a statewide threat.
