Aquatic Nuisance Species

A Threat to Colorado's Waters

Aquatic Nuisance Species (ANS)—including invasive plants, animals and pathogens—pose a serious threat to the health of Colorado’s lakes, reservoirs, rivers and streams. Species such as zebra and quagga mussels, New Zealand mudsnails, Eurasian watermilfoil, Asian carp, rusty crayfish and fish diseases like whirling disease can cause extensive ecological harm, disrupt water infrastructure, and negatively affect recreation and local economies. 

Zebra and quagga mussels are especially concerning for Northern Water due to their ability to rapidly colonize and clog water intakes, pipelines and diversion structures. Once established, these mussels are extremely difficult to remove and can spread quickly via boats, trailers and other watercraft equipment. Alarmingly, zebra mussels have now been detected in West Slope waterbodies downstream of Northern Water’s collection system, underscoring the urgent need for continued vigilance and prevention efforts. 

Four people in vests inspecting a boat on a trailer for aquatic nuisance species.
Protecting Colorado Waters: The ANS Program

Colorado’s Aquatic Nuisance Species (ANS) Program is managed by Colorado Parks and Wildlife (CPW) under the authority of the State ANS Act (SB 09-226). The program plays a critical role in preventing the spread of invasive species through mandatory watercraft inspection and decontamination at more than 70 sites across the state, roadside inspection stations and ongoing public education efforts.

Within Northern Water’s system, all lakes and reservoirs that permit motorized boating are subject to mandatory inspections at every boat launch. This includes the Three Lakes system in Grand County, Horsetooth Reservoir and Carter Lake in Larimer County, and Boulder Reservoir in the City of Boulder—ensuring that these vital waterbodies remain protected from invasive threats.

Sailboats out on a body of water with mountains in the background.
Partnering to Protect Colorado’s Waters

Northern Water works closely with partners on both sides of the Continental Divide to prevent and manage the spread of ANS. Our collaborative efforts include partnerships with Colorado Parks and Wildlife (CPW), Larimer County, Grand County, City of Boulder, U.S. Forest Service and the U.S. Bureau of Reclamation.

Together, we support sustainable recreational boating and ensure the continued operation of critical water delivery systems serving Northeastern Colorado. To strengthen these efforts, Northern Water also provides regular funding to partner agencies, helping safeguard our waterways from the harmful impacts of invasive species.

 

Eurasian Watermilfoil at Boulder Reservoir

In summer 2022, Colorado Parks and Wildlife confirmed the presence of Eurasian Watermilfoil (EWM)—a fast-spreading invasive aquatic plant—in Boulder Reservoir. Since its detection, EWM has become established, with significant growth observed in the western coves and swim beach areas. Its presence has disrupted boating and swimming activities and poses a threat to water infrastructure.

Northern Water is actively partnering with the City of Boulder to develop and implement management strategies aimed at controlling the infestation and protecting reservoir operations. 

City of Boulder’s Aquatic Invasive Species Website
Lady in a wetsuit wearing a hat scrapping Eurasian Water Milfoil into a bucket.