Boulder staff have launched a new effort at Boulder Reservoir to control invasive Eurasian watermilfoil. The plant was first spotted in the reservoir in 2022 and has since covered much of the reservoir’s western coves, displacing native species, creating obstacles for recreationists and potentially causing problems for infrastructure if it spreads further.
After attempts to use an herbicide were abandoned, the city shifted to a diver-based program. The new approach is known as DASH, or diver-assisted suction harvesting.
A diver will pull out Eurasian watermilfoil from the reservoir floor and feed it into a suction tube that pumps the plant matter onto a boat. Another team member separates any accidentally collected native plants or animals and returns them to the water. The milfoil will then be mixed with goose manure, composted and used on reservoir grounds.
The dive boat will be out on the reservoir Monday through Thursday during the summer, said reservoir manager Stacy Cole. Dive flags and signs will also be posted to keep recreationists aware of when work is happening. Efforts are expected to continue into the fall.
Beginning work before summer “is critical to get ahead of plant growth,” said Anna Hermes, a watershed scientist with Northern Water. The utility company shares management responsibilities for Boulder Reservoir with the city.
Much of the work will be done by city staff, with assistance from Wisconsin-based contractor Aquatic Plant Management. The Boulder County Youth Corps will assist with shoreline cleanup, moving plant matter for composting and public education outreach.
Cole said residents with diver certifications are welcome to reach out to the reservoir for volunteer opportunities. “We won’t turn away free help,” she said.
Crews have already completed harvesting work near the reservoir’s swim beach in an effort to improve visitor access and recreation.
