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

According to the announcement, multiple crayfish were found in the lake during routine Aquatic Nuisance Species (ANS) sampling by CPW’s Sampling and Monitoring team near Sunset Point campground on Aug. 17. The crayfish were sent to Pisces Molecular in Boulder for a genetics test and were later confirmed to be rusty crayfish on Aug. 31. 

CPW’s ANS Sampling and Monitoring team along with area aquatic biologists later set several crayfish traps around Lake Granby and other nearby waters overnight on Sept. 11, to determine the extent of the rusty crayfish population. 

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Two of those traps in Lake Granby did contain rusty crayfish but traps from the surrounding waters had none. 

Rusty crayfish are a larger, more aggressive freshwater crayfish, native to the Ohio River Basin. They eat small fish, aquatic insects, eggs and aquatic vegetation that can damage fish habitats for spawning, cover and food. The rusty patches on either side of the crayfish’s body can be an identifier for them. 

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In 2009, the rusty crayfish was detected for the first time in Colorado in the Yampa River and Catamount Reservoir. It was found again in 2010 in Sanchez State Wildlife Area, and again — this time, in Routt County — at Stagecoach Reservoir State Park in 2011. They are believed to have been illegally introduced to Colorado as bait used by anglers.

CPW Invasive Species Program Manager Robert Walters confirmed that this is the first time rusty crayfish have been found in the Upper Colorado River Basin. Lake Granby feeds into the Colorado River, and if rusty crayfish make the journey, they can threaten the entire Colorado River Basin. 

CPW offers four steps to prevent the introduction and spread of invasive species in Colorado: 

• Use bait that is legal in Colorado and never bring live aquatic bait from another state. 
• Do not throw unused bait back in the water if it is alive. 
• Clean gear and water crafts before heading to the next body of water. 
• Do not dispose of pets, plants or animals in natural systems. 

Crayfish of any species are not native west of the Continental Divide. Live transportation of any crayfish from waters west of the Divide is prohibited.

All crayfish caught west of the Continental Divide must be immediately killed by removing the head from the thorax and taken into possession or immediately returned to the water from which they were taken.