CPW confirms presence of rusty crayfish in Little Thompson River
Kara Van Hoose
May 2, 2025
CPW confirms rusty crayfish presence in Little Thompson River
LARMIER COUNTY, Colo. — Colorado Parks and Wildlife has confirmed the presence of rusty crayfish, an aquatic nuisance species, in the West Fork Little Thompson River. This is the first discovery of the rusty crayfish in the Little Thompson River and CPW’s Northeast Region. It is the second time the species has been identified east of the Continental Divide in Colorado.
The non-native crustacean was first reported to CPW by a member of the public through iNaturalist, a species identification app, on April 7. CPW’s ANS Sampling and Monitoring Team performed a follow up survey on April 8. Samples collected by the team were genetically confirmed to be rusty crayfish on April 18. CPW will conduct additional surveys of the Little Thompson River to determine the size and extent of the population in the coming months.
The rusty crayfish is native to the Ohio River basin. It is larger and more aggressive than native crayfish species, often outcompeting them for food and resources. They are classified as a prohibited aquatic nuisance species due to their voracious appetite on critical habitat vegetation and prolific reproduction habits.
“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.”
CPW has confirmed rusty crayfish in five other waterbodies in Colorado, including Lake Granby in August 2023. They have dark black rings near the tips of their claws and eponymous rusty patches on either side of their abdomen. Males can grow up to five inches long. The rusty crayfish can live in pooled or fast water.
The spread of aquatic nuisance species can be stifled by cleaning, draining and drying any watercraft used in the state, even non-motorized vessels. CPW provides required inspections for trailered and motorized watercraft at state parks and wildlife offices. A boater who has launched their vessel outside of Colorado is obligated to tell inspectors in order to prevent the spread of invasive species.
Non-native wildlife or plant species should not be dumped into bodies of water in Colorado. They can negatively impact native species and cause strain on natural resources. Introducing non-native wildlife could contribute to the spread of diseases and parasites.
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Colorado Parks and Wildlife (CPW) is an enterprise agency, relying primarily on license sales, state parks fees and registration fees to support its operations, including: 43 state parks and more than 350 wildlife areas covering approximately 900,000 acres, management of fishing and hunting, wildlife watching, camping, motorized and non-motorized trails, boating and outdoor education. CPW's work contributes approximately $6 billion in total economic impact annually throughout Colorado.
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