Lake Dillon is warming, but its water quality remains OK, study finds

Dillon Reservoir in Summit County, Colorado (Photo by Lars Gesing)

A new environmental study has some rare good news for stressed Colorado water managers: Lake Dillon, the Summit County reservoir that supplies water to much of the Denver metro area, has warmed almost 5 degrees Fahrenheit in the last 35 years — but the water quality has not taken a hit.

That is because the lake’s altitude, 9,000 feet, and the low average temperatures surrounding the lake serve as buffers against problems associated with climate change-induced warming that afflict many water bodies around the globe, says William Lewis, director of the University of Colorado at Boulder’s Cooperative for Research in Environmental Studies and the study’s lead author.

At lower elevations and particularly in the tropics, where temperatures are much higher than Colorado’s, warming waters lead to exploding algae populations and dropping deepwater oxygen levels. That in turn drastically decreases water quality, leading to supply shortages for millions of people around the globe.

Lewis and his fellow researchers have collected detailed information about temperature, water quality and aquatic life in Lake Dillon since 1981. The multi-decade research was sponsored by Denver Water and the Summit Water Quality Committee.

Natural events such as droughts and floods can obscure the impacts of climate change on ecosystems. But “This is an exceptionally long record of lake temperatures for the entire water column of the lake,” Lewis said. “For that reason, it gives us confidence that what we are seeing as a trend is not a short-term variance but actually a reflection of climate change.”

While the study provides a glimmer of hope in a sea of bad news about our changing climate, Lake Dillon continues to give state officials in Colorado headaches. Water quality might not be be declining, but the overall amount of water is, as the state continues to suffer through its record 19th year of drought conditions.

After their sweep in the 2018 midterms, Democratic lawmakers and Gov.-elect Jared Polis have vowed to make climate change and environmental protection a centerpiece of their agenda for the legislative session that just kicked off.


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