Parks and Wildlife discovers large, aggressive crayfish in Lake Granby

First detection in Upper Colorado River Basin poses threat to entire basin's ecosystem

Trapping efforts are being utilized to determine where the rusty crayfish are living.
Colorado Parks and Wildlife/Courtesy photo

Colorado Parks and Wildlife announced the discovery of rusty crayfish in Lake Granby.

In a routine Aquatic Nuisance Species sampling done by Parks and Wildlife, multiple crayfish were found in Lake Granby on Aug. 17. Samples were collected and then preliminary species identification was performed at a laboratory. The suspect specimens were then sent to Pisces Molecular in Boulder to run genetic tests.

The samples were confirmed to be rusty crayfish Aug. 31. 

Parks and Wildlife’s species sampling and monitoring team along with area aquatic biologists then set multiple crayfish traps around Lake Granby and other waters close to the lake. Sampling traps were left overnight during the week of Sept. 11 before being collected.

Crayfish traps collected from the surrounding lakes did not contain crayfish; however two traps from Lake Granby did contain rusty crayfish. 

Aquatic Nuisance Species Sampling and Monitoring team members separating and identifying crayfish from Lake Granby during trapping efforts the week of Sept. 11.
Colorado Parks and Wildlife/Courtesy photo

A trap was also placed below the dam on the Colorado River and upon removal of the trap, officials found no crayfish. 

“While this is not the first time we have found rusty crayfish west of the divide here in Colorado, it is the first detection in the Upper Colorado River basin,” Robert Walters, Colorado Parks and Wildlife’s invasive species program manager, stated in a press release. “While finding any invasive species is detrimental to our state’s aquatic ecosystems, finding rusty crayfish in Lake Granby, which feeds into the Colorado River, poses an even greater threat to the entire Colorado River Basin.”

Rusty crayfish were previously discovered in the Yampa River and Catamount Reservoir in 2009. They are a larger, more aggressive freshwater crayfish and are native to the Ohio River Basin. Their rusty patches on the sides of their body are often used to identify them.

They are believed to have been illegally introduced to Colorado by anglers as bait. 

Parks and Wildlife’s steps to avoid introducing and spreading invasive species
  • Use only bait that is legal in Colorado. Never bring in live aquatic bait from another state.
  • Do not throw unused bait of any kind, back in the water alive.
  • Clean, drain, and dry your gear and water craft before heading to the next body of water.
  • Do not dispose of pets or unwanted aquarium plants or animals in natural systems.

Crayfish of any species are not native west of the Continental Divide and Parks and Wildlife wants to remind the public that the live transportation of all crayfish from waters west of the Continental Divide is prohibited. All crayfish found west of the Continental Divide are to be immediately destroyed.

To learn more about the rusty crayfish and how to prevent the spread of the invasive species, visit Parks and Wildlife’s website.

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