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
South Platte River (just below Eleven Mile dam in Park County)
Positive since 2004
Boulder Creek
Positive since 2004
Green River within Dinosaur National Monument
Positive since 2005
Dry Creek, City of Boulder
South Delaney Buttes State Wildlife Area
Positive since 2010
East Delaney Buttes State Wildlife Area
Positive since 2010
Eleven Mile Reservoir State Park
Positive since 2011
Charlie Meyer State Wildlife Area
Positive since 2011
College Lake, Colorado State University
Positive since 2011
Spinney Mountain State Park
Positive since 2011
Fountain Creek
Positive since 2012
Chatfield Reservoir
Positive since 2013
Gunnison River (West of Delta)
Positive since 2015
Fourmile Canyon Creek (Boulder County)
Positive since 2016
Monument Lake
Positive since 2017
South Platte River (Near Deckers)
Positive since 2017
Uncompahgre River (Town of Montrose)
Positive since 2017
Jimmy Camp Creek
Positive since 2017
Monument Reservoir
Positive since 2018
Trinidad Lake
Positive since 2018
Lake Capote
Positive since 2018
Chatfield Pond #1
Positive since 2019
Elmer’s 2 Mile Park (Boulder County)
Positive since 2019
South Platte River (City of Denver)
Positive since 2019
Trout Creek
Positive since 2020
South Boulder Creek
Positive since 2020
Antero Reservoir
Positive Since 2024
South Platte River (just below Eleven Mile dam in Park County)
Positive since 2004
Boulder Creek
Positive since 2004
Green River within Dinosaur National Monument
Positive since 2005
Dry Creek, City of Boulder
South Delaney Buttes State Wildlife Area
Positive since 2010
East Delaney Buttes State Wildlife Area
Positive since 2010
Eleven Mile Reservoir State Park
Positive since 2011
Charlie Meyer State Wildlife Area
Positive since 2011
College Lake, Colorado State University
Positive since 2011
Spinney Mountain State Park
Positive since 2011
Fountain Creek
Positive since 2012
Chatfield Reservoir
Positive since 2013
Gunnison River (West of Delta)
Positive since 2015
Fourmile Canyon Creek (Boulder County)
Positive since 2016
Monument Lake
Positive since 2017
South Platte River (Near Deckers)
Positive since 2017
Uncompahgre River (Town of Montrose)
Positive since 2017
Jimmy Camp Creek
Positive since 2017
Monument Reservoir
Positive since 2018
Trinidad Lake
Positive since 2018
Lake Capote
Positive since 2018
Chatfield Pond #1
Positive since 2019
Elmer’s 2 Mile Park (Boulder County)
Positive since 2019
South Platte River (City of Denver)
Positive since 2019
Trout Creek
Positive since 2020
South Boulder Creek
Positive since 2020
Antero Reservoir
Positive Since 2024
Yampa River
Positive since 2009
Catamount Reservoir
Positive since 2009
Sanchez State Wildlife Area
Positive since 2010
Stagecoach Reservoir State Park
Positive since 2011
Granby
Yampa River
Positive since 2009
Catamount Reservoir
Positive since 2009
Sanchez State Wildlife Area
Positive since 2010
Stagecoach Reservoir State Park
Positive since 2011
Granby
Adobe Creek SWA
Arkansas River
Arvada Reservoir
Aurora Reservoir
Bear Canyon Creek
Bessemer Ditch
Big Dry Creek
Blue Heron Ponds
Boulder Creek
Boulder Reservoir
Bow Mar Lake
Bowles Reservoir
Brush Hollow Reservoir
Charlie Meyer SWA
Chatfield Reservoir
Cherry Creek Reservoir
CU Ponds in Boulder
Douglas Reservoir
Eleven Mile State Park
Fountain Lake
Gateway Reservoir (Private)
Horseshoe and Martin Reservoirs in Lathrop SP
Lon Hagler Reservoir
Lowell Ponds
Marston Reservoir
Lake Minnequa
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
Lake Pueblo
Pueblo Steel Mill
Rio Grande River
Saint Charles Reservoir #2, #3
Saint Vrain Creek
Saint Vrain State Ponds
Sawhill Ponds
San Isabel Lake
Sheets Lake
Skaguay Reservoir
South Platte River
Standley Lake (Westminster)
Swift Ponds
Tucker Lake
Tule Lakes
Walden Pond
Ward Road Ponds
Wellington Reservoir #4
West Lake
West Prospect Park Lake
Adobe Creek SWA
Arkansas River
Arvada Reservoir
Aurora Reservoir
Bear Canyon Creek
Bessemer Ditch
Big Dry Creek
Blue Heron Ponds
Boulder Creek
Boulder Reservoir
Bow Mar Lake
Bowles Reservoir
Brush Hollow Reservoir
Charlie Meyer SWA
Chatfield Reservoir
Cherry Creek Reservoir
CU Ponds in Boulder
Douglas Reservoir
Eleven Mile State Park
Fountain Lake
Gateway Reservoir (Private)
Horseshoe and Martin Reservoirs in Lathrop SP
Lon Hagler Reservoir
Lowell Ponds
Marston Reservoir
Lake Minnequa
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
Lake Pueblo
Pueblo Steel Mill
Rio Grande River
Saint Charles Reservoir #2, #3
Saint Vrain Creek
Saint Vrain State Ponds
Sawhill Ponds
San Isabel Lake
Sheets Lake
Skaguay Reservoir
South Platte River
Standley Lake (Westminster)
Swift Ponds
Tucker Lake
Tule Lakes
Walden Pond
Ward Road Ponds
Wellington Reservoir #4
West Lake
West Prospect Park Lake
Highline Lake and the Colorado River (in Grand Junction) have tested positive for zebra mussels.
Out of State
Colorado is experiencing a significant increase in the amount of mussel infested boats being intercepted at lakes and reservoirs across the state. While these boats are coming in from all directions, the majority are originating from Lake Powell (72%).
Invasion of mussels from out-of-state waters continues to be a threat, and will likely increase. Almost all states to the east of Colorado have a zebra or quagga mussel infestation. The closest is Cedar Bluff Reservoir which is only 150 miles from our border in Kansas. The southwest US has many widespread infestations including Lake Powell, Lake Mead, Lake Mohave, and Lake Havasu, which are all frequented by Colorado boaters.
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.