Vegetation Management

Controlling Algae and Weeds In and Around Our Waterways 

Northern Water manages aquatic and terrestrial weed and algae control across nearly 50 miles of East Slope canals and adjacent service roads, as well as approximately 5 miles of canals and roads on the West Slope. In addition, our team maintains vegetation on the upstream and downstream faces of seven reservoir dams and dikes: Windy Gap, Willow Creek, Granby, Shadow Mountain, Horsetooth, Carter Lake and Boulder. 

Effective weed control is essential for maintaining canal capacity, preventing blockages in bar screens and flumes, encouraging healthy grass growth, and facilitating dam and dike inspections. Northern Water applies chemical herbicides with precision and care, prioritizing the protection of drinking water sources, aquatic ecosystems, and wildlife. 

Our herbicide applications are regulated under the Colorado Discharge Permit System’s Pesticide General Permit, which governs pesticide discharges to surface waters. Compliance includes developing a Pesticide Discharge Management Plan and submitting annual reports to the Colorado Water Quality Control Division. The plan outlines targeted algae and weed populations, treatment locations, herbicides used and the implementation of technology-based effluent limitations and other permit requirements to safeguard water quality. 

To support this plan, Northern Water operates two monitoring programs: 

• Canal Periphyton Monitoring Program: This program identifies species of attached algae in the canals and tracks changes over time. The data help assess the effectiveness of herbicide treatments in controlling algal growth.
• Compounds of Emerging Concern (CEC) Monitoring Program: This initiative measures trace levels of herbicides that may remain in water following treatment, particularly in the Boulder Feeder Canal. It also monitors for residual herbicides—at parts-per-trillion levels—across the CBT East Slope canals, reservoirs, and receiving waters. These residues may result from applications by Northern Water or other entities throughout the region.