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Aquatic Nuisance Animals

Zebra Mussel (Dreissena polymorpha)

Zebra mussels were found at Lake Pueblo in January 2008. Subsequently six other water bodies are suspected or tested positive for zebra or quagga mussels. Zebra mussels are a non-native invasive species that spread very quickly, having harmful effects on the environment. Zebra mussels attach to hard surfaces and are known to clog intakes and engines on boats, as well as pipes and water transport structures.

All boaters and other water craft recreational users should take simple, precautionary steps – every time they go to a lake, river or stream.

Before leaving a lake or other waterway, boaters should:

  • CLEAN the hull of your boat.

  • DRAIN the water from the boat, live well and the lower unit of the engine.

  • DRY the boat, fishing gear, and equipment.

  • INSPECT all exposed surfaces.

  • REMOVE all plant and animal material.

See the Clean, Drain and Dry brochure (Zebra mussel preventive measure).

In 1988 zebra mussels spread from Eurasia to the Great Lakes in contaminated ballast water. They quickly spread to the Mississippi River, its tributaries and inland lakes. They have not yet  made it west of the 100th meridian. Zebra mussels cost the USA billions of dollars a year in national control efforts!

Zebra mussels are small barnacle-like clams with dark and light colored stripes. They smother aquatic organisms, such as crayfish and native clams and outcompete for food and aquatic habitat. Zebra mussels damage equipment by attaching to boat motors or hard surfaces and clog water treatment facilities. They also litter beaches with sharp, dangerous shells.

Quagga Mussel (Dreissena bugensis)

On January 6, 2007 live Quagga mussels (Dreissena bugensis) were found in Lake Mead, along the Arizona-Nevada border. Quagga mussels are closely related cousins to the well-known, nasty exotic Zebra mussel (Driessena polymorpha). Quagga mussels are native to Eurasia and probably arrived in the USA as hitch hikers in ballast water of ships. Quagga mussels can survive in a wide range of conditions and can thrive where zebra mussels cannot.

This is the first established population west of the continental divide and is approximately 1000 miles west of any previously documented quagga or zebra mussel location. Please clean all gear that comes into contact with the water to avoid introducing quagga mussels or any aquatic nuisance species, into Colorado's waters. For more information, visit 100th Meridian Initiative.

New Zealand Mudsnail (Potamopyrgus antipodarum)

New to Colorado in 2004! New Zealand Mudsnails (NZMS) were first found in the USA in the late 1980's in Snake River, ID and Madison River, MT. These tiny mollusks quickly spread to Yellowstone National Park. They were first found in CO in Boulder Creek in 2004. The second CO sighting was in the upper South Platte River, just outside Eleven Mile SP in 2005. This prolific invader is going to require everyone's attention to stop the spread!

NZMS here are female clones and prefer fast moving river waters and all substrates. Reproduction is asexual: it only takes 1 to survive! The snails average 1/8" in length with cone shaped shells containing 5-6 whorls. The shell of the New Zealand mud snail is narrower, longer and has more whorls than most native snails.

New Zealand mudsnails are relatively small (average length of 4-5 mm in western USA), with a maximum of 11 mm in native habitats. The adult New Zealand mudsnail can be confused with various similar looking native and exotic species so identification should be verified by the Resource Stewardship team. The shell of the New Zealand mud snail is narrower, longer, and has more whorls than most hydroid snails native to the United States.

Fisherman! Protect your fisheries! Clean Your Gear! Be sure to remove all visible mud and plant fragments from your gear before leaving a water body and entering a new water system. Anything that comes in contact with the water can spread the snail from one body of water to another!

For more information, visit the Montana State University's New Zealand Mudsnail page or The Western Regional Panel.

Aquatic Noxious Weeds

Eurasian watermilfoil (Myriophyllum spicatum)

State B List Noxious Weed

Eurasian watermilfoil (EWM) is native to Europe, Asia and Northern Africa. EWM is a highly invasive aggressive species that colonizes a variety of habitats. EWM forms extremely dense monotypic stands due to it’s rapid growth rate (1 ft/wk). Dense mats crowd out native species, disrupt the food chain and displace wildlife habitat. Dense mats disrupt all forms of water-based recreation including boating, swimming and fishing.

EWM is a submerged, rooted perennial dicot. Plants have pink to olive-green stems. Stems branch several times in the water column. Leaves are feathery, dark green and often arranged in whorls of 4, but can be in whorls of 3-5. Each leaf has 12 or more pairs of leaflets on either side of the midrib. Leaves are typically 0.5-2.0 inches long. Small reddish-brown flower spikes emerge above the waters surface from June through September. 

Beware of the native look-alike, Northern watermilfoil (Myriophyllum sibiricum):

The exotic species has 12 or more pairs of leaflets while the native has 10 or less pairs of leaflets. The leaflets on the exotic species are much more closely spaced than the native and the exotic tends to go limp out of water while the native species stays stiff.

Water Hyacinth (Eichhornia crassipes)

New Invader - Beware! This species recently found in the San Luis Valley in 2006 - Be alert to stop the spread!

Water Hyacinth is on the noxious weed list in both Arizona and California, but not in Colorado. It is considered one of the most destructive weeds of western waterways!

The seedlings of water hyacinth usually root in mud and then break free and float as they mature. Typically mature plants float and are linked together by stolons. Leaves are smooth, basal, floating and submerged.  Leaves are lanceolate, sometimes heart shaped. Roots are feathery, 1+ m long. Flowers spikes bloom above the surface from June-October. Flowers are pale blue, lilac or white.

Hydrilla (Hydrilla verticillata)

State A List Noxious Weed

Hydrilla is native to India and Korea. Hydrilla is able to establish itself in deeper waters where native plants don't normally grow. Eventually, it will spread to shallow water and displace native vegetation. Sport-fish in infested waters are usually reduced in weight and size due to hydrilla altering the natural foraging mechanisms. Dense mats obstruct boating, fishing and swimming in deep and shallow water.

Hydrilla is a submerged, rooted, perennial. It has slender ascending stems to 9m long, heavily branched. Leaves are whorled, 5 per whorl, bearing coarse visible teeth along the margins and usually 1-4 small conical bums along the underside of midrib, which is often red.

Hydrilla is not yet in Colorado and we must remain on alert to prevent this introduction into our waters!

Giant Salvinia (Salvinia molesta)

State A List Noxious Weed

Native to South America (southeastern Brazil). This floating fern forms dense mats that cover the waters surface. Infested waters can not be used for any type of water recreation due to dense surface cover. Dense mats block sunlight and oxygen from penetrating the water, which disrupts the food chain and can potentially cause large fish kills. Giant Salvinia threatens cultivated aquatic crops, clogs irrigation canals and drinking water lines and fouls hydroelectric plants.

Free-floating fern with small oblong, spongy green leaves along the stem. Leaves occur in whorls of 3 = 2 floating leaves and 1 submerged leaf. Young plants have leaves that lie flat on the surface. Older plant leaves become thick and curled at edges forming upright chains that form mats of floating plants.

Giant Salvinia is not yet in Colorado and we must remain on alert to prevent this introduction into our waters!