From Northern Water:
Northern Water, the U.S. Forest Service, the U.S. Bureau of Reclamation, Grand County and additional regional health, water and recreation officials are closely monitoring a potentially harmful algal bloom that developed at Willow Creek Reservoir in July, a component of the Colorado-Big Thompson Project in Grand County.
In late July, monitoring teams found the presence of blue-green algae (cyanobacteria), which can sometimes produce toxins (cyanotoxins) that can be harmful to humans and animals. With this discovery, the U.S. Forest Service’s Arapaho National Forest placed restrictions on water contact recreation and posted signs informing the public of the issue.
Recent tests indicate the concentration of cyanotoxins in the two samples collected to be nearly negligible. However, because of evidence of algae in other parts of the reservoir where sampling has not occurred the reservoir remains under the existing restrictions for contact recreation.
Willow Creek Reservoir is part of the collections system for the Colorado-Big Thompson Project, which gathers water in the headwaters of the Colorado River for delivery to cities, farms and industries in northeast Colorado.
In the East Troublesome Fire of 2020, as much as 90 percent of the watershed that feeds into the reservoir sustained damage. This summer, the arrival of monsoonal moisture has increased the delivery of nutrients from the burn scar to the reservoir, and made these nutrients available to support increased growth of all kinds of algae. However, the vast majority of algae species are not harmful. Water recreation enthusiasts can learn more by viewing the Colorado Parks and Wildlife video and visiting the Colorado Department of Public Health and Environment links available from Grand County.
Water from Willow Creek Reservoir is pumped intermittently into Lake Granby to make room in Willow Creek Reservoir should future flooding occur. However, with a maximum capacity of 10,600 acre-feet, Willow Creek Reservoir is dwarfed by the 540,000 acre-foot Lake Granby, meaning the overall impact to the region’s water supply is negligible. In addition, water quality testing equipment installed in the aftermath of the East Troublesome Fire will be able to monitor key water quality metrics in the Colorado-Big Thompson Project. A monitoring program has been implemented to watch for algae blooms and potential toxins in the Three Lakes, as well as in Willow Creek Reservoir. Agencies will continue to review data and monitor the issue until the bloom disappears.
For information about water recreation opportunities on the Arapaho National Forest, visit http://www.fs.usda.gov/arp.
A joint press release among Northern Water, U.S. Forest Service, U.S. Bureau of Reclamation and Grand County.