Northern Colorado has been getting baked by summer heat, and that’s driving an increase of potentially toxic algae blooms in reservoirs. Colorado Parks and Wildlife says routine inspections of water bodies have alerted them to algae blooms in a handful of area reservoirs, especially in the Northeast part of the state. That has resulted in the closure of two swimming spots.
Last week, CPW closed swimming areas at Cherry Creek State Park and North Sterling State Park. Kara Van Hoose, a spokesperson for the agency, said the closures are meant to keep people and pets from getting into contact with the toxic blue-green algae.
“It can cause skin irritation, rashes, gastrointestinal problems, vomiting, fever, just a lot of things that you don't want to experience,” Van Hoose said. “And for dogs, if it's ingested, it can become fatal.”
Most algae blooms are not considered toxic. To determine toxicity, state wildlife authorities collect water samples to test if particles of the “microcystin” toxin reach a level considered unsafe by the state health department.
Algae blooms have also been found at Jackson Lake State Wildlife Area, Prewitt State Wildlife Area, Vega State Park and Jumbo State Wildlife Area in Julesburg, but those lakes have not been deemed toxic and therefore there haven't been any changes to the recreation rules at those parks.
Even when bodies of water have too much toxic algae to allow swimming or paddleboarding, CPW still allows boating, sailing and kayaking, which are less likely to put toxic water in contact with people’s skin.
Van Hoose said algae blooms are fairly common during the summer. Direct sunlight and warmer water create an environment where algae can thrive. Polluted stormwater runoff can add nutrients to the water and help algae grow even faster.
There is no quick fix for algae growth.CPW typically takes water samples every one or two weeks until the amount of toxins drops back into the safe range.
Since 2021, scientists have expanded blue-green algae research at Blue Mesa Reservoir, Colorado’s largest body of water. The U.S. Geological Survey is combining data from samples on the ground with satellite images to get a better understanding of how the algae grows and spread.
The planet’s warming climate threatens to bring blue-green algae to Colorado’s reservoirs more frequently, and other types of algae to places where it previously couldn’t survive at all. Rising temperatures have driven an increase in the amount of nutrients in high-altitude lakes and ponds, increasing the amount of algae in places such as Rocky Mountain National Park.
Other Colorado reservoirs and swimming areas, including some not owned by CPW, have also experienced problematic algae this summer and over the past few years.
Windsor Lake, which is operated by the town of Windsor, was closed for over a week in July after a test showed the reservoir may have contained blue-green algae.
Cherry Creek State Park, which is in Aurora, has seen a few other unrelated closures this summer. In July, the park’s swimming beach was closed due to unsafe levels of the E. coli bacteria. In June, some park facilities were closed due to high water levels after abnormally heavy rainfall.
This story is part of ongoing coverage of the water in the West, produced by KUNC and supported by the Walton Family Foundation.
