DENVER (KDVR) — Colorado Parks and Wildlife recently discovered an invasive species in Lake Granby.

According to CPW, multiple crayfish were found at the lake during a routine Aquatic Nuisance Species sampling on Aug. 17. On Aug. 31, the samples were confirmed to be rusty crayfish.

After discovering the existence of the invasive species, CPW rangers and area aquatic biologists set traps around Lake Granby, below the dam on the Colorado River and around other lakes that are in close proximity to determine if the species was present in other waters.

CPW said the traps in the surrounding lakes did not contain crayfish, and the trap below the Colorado River dam was empty as well.

  • CPW rusty crayfish 3
  • CPW rusty crayfish 2
  • CPW rusty crayfish 3

What is a rusty crayfish?

According to CPW, rusty crayfish are larger, more aggressive freshwater crayfish. They are native to the Ohio River Basin.

The crayfish have rusty patches on the side of their body that help identify them.

They were first discovered in Colorado in the Yampa River and Catamount Reservoir in 2009.

CPW said they are believed to have been introduced to Colorado by anglers who used them as bait.

“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,” said Robert Walters, CPW’s Invasive Species program manager. “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.” 

Crayfish are not native west of the continental divide. Therefore, CPW is reminding the public that live transportation of crayfish from waters west of the divide is prohibited.

Any crayfish caught west of the divide must be killed and taken into possession.