News Release

Toxic Algae detected in Blue Mesa Reservoir

Date: August 13, 2026

GUNNISON, Colo. – Throughout the summer, National Park Service staff sample and analyze the Blue Mesa Reservoir water for the presence of blue-green algae containing cyanotoxins. At this time, toxic algae have been detected at low levels in the Iola Basin. These levels are under the State of Colorado toxicity threshold. The Iola Basin has been posted with yellow caution signs—consistent with State of Colorado and U.S. Environmental Protection Agency guidance.

Due to shifting winds and currents, areas around the Iola Basin of Blue Mesa Reservoir may have blue-green algae blooms, and caution signs have been distributed to heavily-used visitor areas in the basin. Park staff advise avoiding areas with observed or suspected blue-green algal mats throughout the reservoir. 

If algal toxins reach levels harmful to human and animal health, red warning signs will be posted, consistent with State of Colorado and EPA guidance.

Harmful algae, a type of blue-green algae, are common and natural to our waters and are found throughout Colorado. Algae can multiply rapidly to form blooms and scums, particularly in areas of shallow, warm water. Certain types of algal blooms can produce toxins called cyanotoxins, which can be harmful to humans and animals.   

Boating and fishing remain open throughout Blue Mesa. Be sure to clean harvested fish with treated (potable) water. As always, remember to clean, drain, and dry, all boats and fishing gear.

Water-quality monitoring staff continue to sample critical visitor use areas and are monitoring conditions. Check the park website for updates at www.nps.gov/cure.  

-NPS-

About the National Park Service.  Established in 1916, the National Park Service preserves America’s most treasured natural and cultural places for the enjoyment, education and inspiration of current and future generations. Learn more at nps.gov.