C-BT and WG Water Quality

Comprehensive Water Quality Monitoring Across Our Systems

The Colorado-Big (C-BT) Thompson and Windy Gap project service area covers more than 2,574 square miles, including an extensive network of lakes, reservoirs, rivers and canals. Protecting water quality across this system is vital—not just for drinking and recreation, but also for supporting aquatic life and healthy fish habitats. To safeguard these resources, Northern Water runs robust monitoring programs that track and assess water quality throughout our system. These efforts ensure the water we deliver meets rigorous standards and remains safe, reliable, and sustainable for all uses. 

View Water Quality Data
Water quality monitoring on Horsetooth Reservoir

Baseline Water Quality Monitoring 

Northern Water’s Baseline Water Quality Monitoring Program provides one of the most comprehensive long-term water quality datasets in northern Colorado. Since 1991, Northern Water has monitored lakes, reservoirs, rivers, streams and canals associated with the C-BT and Windy Gap projects, building a high-quality dataset that supports water management and protects drinking water supplies for more than 1.1 million people. 

The program includes year-round monitoring at 55 locations across eight watersheds on both sides of the Continental Divide. Sampling occurs at 41 flowing-water sites (rivers and canals) and 14 lake and reservoir sites, providing a detailed understanding of water quality conditions throughout the system. 

By maintaining a consistent, scientifically rigorous monitoring network, Northern Water takes a proactive approach to identifying water quality concerns, evaluating solutions, and ensuring the continued protection of critical water supplies and aquatic resources. 

C-BT and Windy Gap Water Quality Monitoring Program
Man standing on a buoy in the middle of a lake, which is used for water quality.

Three Lakes Monitoring 

The Three Lakes system—comprising Lake Granby, Shadow Mountain Reservoir and Grand Lake—is a critical component of the C-BT Project’s collection system in the Upper Colorado River Basin. Since 2008, Northern Water has conducted extensive monitoring in these water bodies, with targeted efforts to address specific concerns such as water clarity in Grand Lake. Data collected from the Three Lakes system are integrated into the broader C-BT and Windy Gap monitoring programs to track changes over time and support informed, long-term water management. 

Shadow Mountain Real-Time Monitoring Program
 
Secchi Monitoring Program
 
Three Lake Inlets Temperature and Specific Conductivity Monitoring Program
A small post sticking up around prairie grass and rocks noting a Syntex well.

Syntex Monitoring

Northern Water monitors groundwater near the former Syntex Landfill northwest of Longmont to provide early warning if contamination is moving toward the St. Vrain Supply Canal. Monitoring wells track indicators such as chloride, total dissolved solids and volatile organic compounds. Results to date show no evidence of contaminants nearing the canal.  

Syntex Monitoring Program