Aquatic Nuisance Species (ANS) at the Boulder Reservoir

Eurasian Watermilfoil, an aquatic invasive plant species, has been detected at Reservoir

Colorado Parks and Wildlife has confirmed the presence of Eurasian watermilfoil (EWM), an invasive plant, in the Boulder Reservoir during a semi-annual invasive species monitoring visit in August 2022. If it becomes established, EWM grows quickly, forms thick mats and disrupts aquatic ecosystems.

The invasive plant is not harmful to humans.

With this discovery, the city will work closely with Colorado Parks and Wildlife this fall to determine whether the plant has been established in the Reservoir.

Regarding additional types of ANS, we know that there are New Zealand Mud Snails within walking distance of the Reservoir, and Zebra/Quagga Mussels within driving distance.

We will continue our existing ANS program so that we can protect water quality and recreation access to Boulder Reservoir.

Eurasian watermilfoil

Eurasian Watermilfoil (EWM) at the Reservoir

EWM may have arrived at the Reservoir via wind, fishing, animals, humans or watercraft. This plant can easily be transmitted without the carrier’s knowledge.

If EWM establishes and spreads at the Reservoir, the following services could be impacted:

  • Swimming – Dense plant growth could limit swimming opportunities. As of now, the plant has not been observed in the Reservoir’s swim beach area.
  • Large and small watercraft – EWM can get tangled in boat propellers and engines, which can increase its spread. Dense growth can also make paddle craft use difficult.
  • Adjacent bodies of water – EWM may also spread to nearby Coot Lake which would impact fishing. Since EWM is already present in Boulder Creek and several other bodies of water in Boulder County, the impact to these is minimal.
  • Drinking water – The Reservoir is a water supply jointly managed by the city and Northern Water. EWM can cause taste and odor issues in drinking water and clog water intakes and outlets. The Boulder Reservoir Water Treatment Plant primarily treats water directly from Carter Lake through a pipeline. However, the Reservoir serves as a water supply for the region and a backup water supply for the city, so Northern Water and the city are partnering on planning and future management.

As of August 2022, the city and Northern Water are not planning to make any changes to water supply operations or recreation activities at the Reservoir. The city will continue to run its existing watercraft inspection and decontamination program and implement the following additional precautionary measures to minimize EWM’s spread and educate Reservoir visitors:

  • City staff will continue to inspect large watercraft exiting the Reservoir. Boaters will receive a blue paper receipt indicating that their boat was last inspected at an ANS-positive body of water.
  • City staff will inspect small watercraft exiting the Reservoir, as allowed, and educate visitors about EWM.
  • Watercraft are not allowed on the North shore. Anyone with watercraft or a flotation device in this area and around Coot Lake will be issued a summons with a potential fine.
  • Signage about EWM will be posted around the Reservoir.

With more information from Colorado Parks and Wildlife’s follow-up survey, the city will evaluate EWM mitigation strategies or future adjustments to recreation and water utilities operations.

We will post more information after we receive the results of Colorado Parks and Wildlife's survey.

Aquatic Nuisance Species

Help Protect Our Water Resources

Please help us protect our water resources from the spread of additional harmful plants, animals and other organisms by properly cleaning and de-contaminating your boat, trailer and other personal gear prior to arriving at the Boulder Reservoir (and before using your equipment in other waterways).

Invasive, non-native species of aquatic plants, animals and organisms are increasingly being transported between bodies of water in Colorado and across the U.S. by unsuspecting boaters and other waterway users. Many of these "aquatic hitchhikers" cause serious impacts on our fisheries, eco-systems and water supplies.

These aquatic nuisance species can hitch a ride on our clothing, boats and items used in the water. When we go to another lake or stream, the nuisance species can be released. And, if the conditions are right, these introduced species can become established, creating undesirable consequences.

These hitchhikers can reduce game fish populations, ruin boat engines and jam steering equipment, make lakes/rivers unusable by boaters and swimmers, dramatically impact the operations of drinking water plants, power plants and dams and reduce native species, degrade ecosystems, affect human health and reduce property values.

It's essential that everyone who enjoys boating, fishing and other types of water recreation, take proper care in cleaning all equipment and disposing of all live bait and aquatic pets.

Do not release or discard plants, fish or animals into a body of water.

Aquarium and Aquatic Pets: Do not release anything from a personal aquarium (water, plants, fish or animals) into or near any body of water or storm drain. Explain to your children how this could harm streams and lakes around the country and potentially kill other fish and animals that already live in the water.

Live Bait: Whether you have obtained bait at a store or from another body of water, do not release unused bait into any body of water. If you do not plan to use the bait in the future, dump the bait in a trashcan or bury it on land, at least several hundred feet away from any body of water or storm drain. Also, be aware of any bait regulations, because in some waters, it is illegal to use live bait.