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Aquatic Nuisance Species - Eurasian Watermilfoil
Invasive Wildlife
Aquatic Nuisance Species
Aquatic nuisance species (ANS) are invasive plants and animals that harm lakes, reservoirs, rivers and streams; invasive species can also include non-native viruses and parasites that cause disease in fish. ANS do damage to not just Colorado’s native species, but its economy, public health, property values and parks.
Threats to Colorado
Zebra and Quagga Mussels
Zebra, quagga and golden mussels are considered the most serious threat to Colorado’s waters. They attach themselves in large, densely packed groups to water storage, treatment and distribution systems, causing clogs and other disruptions. This causes devastating problems for municipal, agricultural and industrial infrastructure.
New Zealand Mudsnails
New Zealand mudsnails are an invasive freshwater snail. Being voracious eaters that reproduce rapidly, they deplete aquatic habitats of food for native species, damaging ecosystems in the process. Aquatic insect larvae, native snails and fish are all affected. These mudsnails are also able to pass through a fish's digestive system unharmed, leaving the fish malnourished — and the mud snail free to eat, reproduce and do more damage to the surrounding habitat.
Rusty Crayfish
Rusty crayfish are native to the Ohio River Basin, and may have been introduced to Colorado by anglers using them as bait. Being larger and more aggressive, they outcompete native crayfish for food and habitat. These crayfish will eat aquatic insects, small fish and fish eggs. They also eat aquatic vegetation, which native fish rely on for spawning, cover and food.
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Eurasian Watermilfoil
Eurasian watermilfoil (EWM) is an aquatic noxious weed that forms dense mats on the water’s surface, which restrict swimming, fishing and boating. The mats shade and choke out native aquatic plants that aquatic fish and animals rely on for shelter, habitat and food. The decaying plants foul beaches and decrease oxygen levels in the water, destroying habitat and food for fish and birds. The mats slow the flow of water in ditches, rivers and streams, creating ideal mosquito habitat. EWM clogs water intakes and alters water chemistry, changing the taste and smell of drinking water. EWM reproduces by seeds, fragmentation and winter buds. Any plant fragment can start a new infestation.
Infected Waters in Colorado
Antero Reservoir
Positive Since 2024
Arkansas River (from the confluence with Badger Creek to Hayden Creek Rd)
Positive since 2021
Bear Creek (from Evergreen Reservoir to Bear Creek Reservoir)
Positive since 2023
Badger Creek
Positive since 2021
Boulder Creek
Positive since 2004
Brush Creek (from the Eagle River to its east and west forks)
Positive since 2023
Charlie Meyer State Wildlife Area
Positive since 2011
Chatfield Pond #1
Positive since 2019
Chatfield Reservoir
Positive since 2013
College Lake, Colorado State University
Positive since 2011
Colorado River (from Rifle to the confluence with Big Wash)
Positive since 2022
Dotsero Ponds
Positive since 2025
Dry Creek, city of Boulder
Dry Creek (from the confluence with Boulder Creek to Baseline Reservoir)
Eagle River (from the confluence with Milk Creek to the confluence with the Colorado River)
Positive since 2023
East Delaney Buttes State Wildlife Area
Positive since 2010
Eleven Mile Reservoir State Park
Positive since 2011
Elmer’s 2 Mile Park (Boulder County)
Positive since 2019
Fountain Creek
Positive since 2012
Fourmile Canyon Creek (Boulder County)
Positive since 2016
Grand Valley Water Users Canal
Positive since 2022
Goose Creek
Positive since 2020
Green River within Dinosaur National Monument
Positive since 2005
Gunnison River, West of Delta
Positive since 2015
Jimmy Camp Creek
Positive since 2017
Lake Capote
Positive since 2018
Monument Lake
Positive since 2017
Monument Reservoir
Positive since 2018
Poudre River (from I-25 to the confluence with the South Platte River)
Positive since 2023
Redtail Lake
Positive since 2024
South Boulder Creek
Positive since 2020
South Delaney Buttes State Wildlife Area
Positive since 2010
South Platte River, city of Denver
Positive since 2019
South Platte River (just below Eleven Mile dam in Park County)
Positive since 2004
South Platte River (near Deckers)
Positive since 2017
South Platte River (various locations from Spinney Mountain Reservoir to Henderson)
Positive since 2005
Spinney Mountain State Park
Positive since 2011
Sutherland Ditch
Positive since 2020
Trinidad Lake
Positive since 2018
Trout Creek
Positive since 2020
Turkey Creek (from Bear Creek Reservoir south until it forks)
Positive since 2024
Uncompahgre River, town of Montrose
Positive since 2017
Wonderland Creek
Positive since 2020
Antero Reservoir
Positive Since 2024
Arkansas River (from the confluence with Badger Creek to Hayden Creek Rd)
Positive since 2021
Bear Creek (from Evergreen Reservoir to Bear Creek Reservoir)
Positive since 2023
Badger Creek
Positive since 2021
Boulder Creek
Positive since 2004
Brush Creek (from the Eagle River to its east and west forks)
Positive since 2023
Charlie Meyer State Wildlife Area
Positive since 2011
Chatfield Pond #1
Positive since 2019
Chatfield Reservoir
Positive since 2013
College Lake, Colorado State University
Positive since 2011
Colorado River (from Rifle to the confluence with Big Wash)
Positive since 2022
Dotsero Ponds
Positive since 2025
Dry Creek, city of Boulder
Dry Creek (from the confluence with Boulder Creek to Baseline Reservoir)
Eagle River (from the confluence with Milk Creek to the confluence with the Colorado River)
Positive since 2023
East Delaney Buttes State Wildlife Area
Positive since 2010
Eleven Mile Reservoir State Park
Positive since 2011
Elmer’s 2 Mile Park (Boulder County)
Positive since 2019
Fountain Creek
Positive since 2012
Fourmile Canyon Creek (Boulder County)
Positive since 2016
Grand Valley Water Users Canal
Positive since 2022
Goose Creek
Positive since 2020
Green River within Dinosaur National Monument
Positive since 2005
Gunnison River, West of Delta
Positive since 2015
Jimmy Camp Creek
Positive since 2017
Lake Capote
Positive since 2018
Monument Lake
Positive since 2017
Monument Reservoir
Positive since 2018
Poudre River (from I-25 to the confluence with the South Platte River)
Positive since 2023
Redtail Lake
Positive since 2024
South Boulder Creek
Positive since 2020
South Delaney Buttes State Wildlife Area
Positive since 2010
South Platte River, city of Denver
Positive since 2019
South Platte River (just below Eleven Mile dam in Park County)
Positive since 2004
South Platte River (near Deckers)
Positive since 2017
South Platte River (various locations from Spinney Mountain Reservoir to Henderson)
Positive since 2005
Spinney Mountain State Park
Positive since 2011
Sutherland Ditch
Positive since 2020
Trinidad Lake
Positive since 2018
Trout Creek
Positive since 2020
Turkey Creek (from Bear Creek Reservoir south until it forks)
Positive since 2024
Uncompahgre River, town of Montrose
Positive since 2017
Wonderland Creek
Positive since 2020
Catamount Reservoir
Positive since 2009
Granby Reservoir
Positive since 2023
Sanchez State Wildlife Area
Positive since 2010
Stagecoach Reservoir State Park
Positive since 2011
West Fork Little Thompson River (West of US-36, along County Road 47)
Positive since 2025
Yampa River
Positive since 2009
Catamount Reservoir
Positive since 2009
Granby Reservoir
Positive since 2023
Sanchez State Wildlife Area
Positive since 2010
Stagecoach Reservoir State Park
Positive since 2011
West Fork Little Thompson River (West of US-36, along County Road 47)
Positive since 2025
Yampa River
Positive since 2009
Adobe Creek SWA
Arkansas River
Arvada Reservoir
Aurora Reservoir
Bear Canyon Creek
Beckwith Reservoir
Positive since 2022
Bessemer Ditch
Big Dry Creek
Blue Heron Ponds
Boulder Creek
Boulder Reservoir
Bow Mar Lake
Bowles Reservoir
Brush Hollow Reservoir
Charlie Meyer SWA
Chatfield Ponds
Positive since 2012
Chatfield Reservoir
Cherry Creek Reservoir
Cigar Pond
Positive since 2004
Conejos River (From the confluence with the Rio Grande River to State Highway 17)
Positive since 2012
CU Ponds in Boulder
Douglas Reservoir
Eleven Mile State Park
Excelsior Ditch
Positive since 2012
Fountain Lake
Gateway Reservoir (Private)
Golden Gravel Ponds (#1,2,3)
Positive since 2012
Horseshoe and Martin Reservoirs in Lathrop SP
Lake Pueblo
Lake Minnequa
Last Chance Ditch
Leggett Ditch
Lon Hagler Reservoir
Lowell Ponds
Marston Reservoir
Minnequa Canal (Fremont Canal)
Monument Lake
Navajo Reservoir (NM Side)
North Poudre Reservoir #4
Palmer Lake
Panama Reservoir #1
Pathfinder Park Pond
Pavlakis Open Space
Pella Crossing Ponds
Prospect Lake
Pueblo Steel Mill
Quincy Reservoir
Positive since 2022
Rio Grande River
Saint Charles Reservoir #2, #3
Saint Vrain Creek
Saint Vrain State Ponds
Salt Creek (From the confluence with the Arkansas River to Saint Charles Reservoirs)
Positive since 2013
San Isabel Lake
Sawhill Ponds
Sheets Lake
Skaguay Reservoir
South Platte River
Standley Lake (Westminster)
Swift Ponds
Tucker Lake
Tule Lakes
Valco Ponds
Positive since 2017
Walden Pond
Ward Road Ponds
Wellington Reservoir #4
West Lake
West Prospect Park Lake
Whiterock Ditch
Windsor Reservoir
Positive since 2015
Adobe Creek SWA
Arkansas River
Arvada Reservoir
Aurora Reservoir
Bear Canyon Creek
Beckwith Reservoir
Positive since 2022
Bessemer Ditch
Big Dry Creek
Blue Heron Ponds
Boulder Creek
Boulder Reservoir
Bow Mar Lake
Bowles Reservoir
Brush Hollow Reservoir
Charlie Meyer SWA
Chatfield Ponds
Positive since 2012
Chatfield Reservoir
Cherry Creek Reservoir
Cigar Pond
Positive since 2004
Conejos River (From the confluence with the Rio Grande River to State Highway 17)
Positive since 2012
CU Ponds in Boulder
Douglas Reservoir
Eleven Mile State Park
Excelsior Ditch
Positive since 2012
Fountain Lake
Gateway Reservoir (Private)
Golden Gravel Ponds (#1,2,3)
Positive since 2012
Horseshoe and Martin Reservoirs in Lathrop SP
Lake Pueblo
Lake Minnequa
Last Chance Ditch
Leggett Ditch
Lon Hagler Reservoir
Lowell Ponds
Marston Reservoir
Minnequa Canal (Fremont Canal)
Monument Lake
Navajo Reservoir (NM Side)
North Poudre Reservoir #4
Palmer Lake
Panama Reservoir #1
Pathfinder Park Pond
Pavlakis Open Space
Pella Crossing Ponds
Prospect Lake
Pueblo Steel Mill
Quincy Reservoir
Positive since 2022
Rio Grande River
Saint Charles Reservoir #2, #3
Saint Vrain Creek
Saint Vrain State Ponds
Salt Creek (From the confluence with the Arkansas River to Saint Charles Reservoirs)
Positive since 2013
San Isabel Lake
Sawhill Ponds
Sheets Lake
Skaguay Reservoir
South Platte River
Standley Lake (Westminster)
Swift Ponds
Tucker Lake
Tule Lakes
Valco Ponds
Positive since 2017
Walden Pond
Ward Road Ponds
Wellington Reservoir #4
West Lake
West Prospect Park Lake
Whiterock Ditch
Windsor Reservoir
Positive since 2015
Colorado River (From 32 Road bridge downstream to the Colorado-Utah border)
Infested since 2024
Colorado River (From the confluence with the Roaring Fork River to 32 Road bridge in Grand Junction)
Positive since 2024
Highline Lake
Infested since 2022
Mack Mesa Lake (at Highline Lake State Park)
Infested since 2025
Private Body of Water (Eagle County)
Infested since 2025
West and East Lake (at the Wildlife Area Section of James M. Robb - Colorado River State Park)
Infested since 2025
Colorado River (From 32 Road bridge downstream to the Colorado-Utah border)
Infested since 2024
Colorado River (From the confluence with the Roaring Fork River to 32 Road bridge in Grand Junction)
Positive since 2024
Highline Lake
Infested since 2022
Mack Mesa Lake (at Highline Lake State Park)
Infested since 2025
Private Body of Water (Eagle County)
Infested since 2025
West and East Lake (at the Wildlife Area Section of James M. Robb - Colorado River State Park)
Infested since 2025
Protect Colorado's Waters
Invasive species of plants and wildlife harm Colorado's land and water, negatively impacting the state’s economy, recreation, property values and public health. Invasive wildlife spread by hitchhiking on watercraft, trailers, vehicles, tires, boots, waders, equipment, gear, firewood and even dogs! Cleaning gear before and after use can help prevent the spread of aquatic nuisance species.