City Expands Effort to Remove Eurasian Watermilfoil from Boulder Reservoir

This week, the City of Boulder and Northern Water launched new management efforts to help remove Eurasian Watermilfoil (EWM), an invasive aquatic plant species, at the Boulder Reservoir.

EWM was initially detected at the Boulder Reservoir in summer 2022 by Colorado Parks and Wildlife. Since then, the city and Northern Water have worked together to remove the invasive plant in shallow areas and have now expanded to more intensive mechanical and manual removal efforts.

Now through October, reservoir visitors can expect to see the following removal methods taking place on the water:

• Diver Assisted Suction Harvesting (DASH Program): an operation where divers use suction tubes underwater to remove EWM at the roots, reducing the plant population over time. Divers plan to operate in the water Mondays through Thursdays.
• Mechanical Harvesting: an approach that removes EWM biomass by cutting the plants underwater, similar to mowing, and collecting the material for removal. Contracted mechanical harvesting dates are scheduled now through June 9 and from Sept. 21 through Oct. 9.
• Shoreline Cleanup: The Mile High Youth Corps will support city staff with shoreline cleanup by manually removing near-shore EWM and collecting plant fragments and other shoreline debris.

The majority of these operations will take place within the no wake zone of the reservoir. Signage will be posted at the reservoir entrance gate and boat ramps to serve as a reminder for boaters to exercise caution when removal operations are actively in progress. Additionally, diver locations will be indicated with "diver-down flags."

In partnership with Eco-Cycle, the city launched an on-site composting program in 2025 to support sustainable invasive species management. As part of this effort, harvested EWM will be combined with goose waste to reduce landfill disposal and create nutrient-rich compost for future use on turfgrass areas at the reservoir.

While removal efforts help contain the plant, preventing the spread to and from the reservoir remains critical. "Preventing the spread of invasive aquatic plant species is a shared responsibility," said Reservoir Recreation Manager, Stacy Cole. "We encourage all reservoir visitors to continue practicing the 'Clean, Drain, Dry' approach by cleaning all watercraft and gear, draining all water and allowing equipment to fully dry before entering another waterway."

Boulder Reservoir remains open and welcoming to visitors throughout the removal process. The water is beautiful, the recreation is world-class, and the community's commitment to protecting this resource makes it even more special. Whether you're planning a morning paddle, an afternoon swim, or a day on the water with family and friends, now is a great time to come out and enjoy everything the Reservoir has to offer. Visitors are encouraged to check the Boulder Reservoir recreation page for current conditions, hours, and registration information before heading out.

Boulder Reservoir also serves as a water supply for the city of Boulder as well as communities and water users downstream of the facility. More information on the city and Northern Water's EWM management plan can be found on the FAQ webpage.