As weather warms, algae blooms on waterways nationwide

With views of the Rocky Mountains, the occasional squadron of American white pelicans passing through, and a boardwalk for strolling, northern Colorado’s Windsor Lake is a popular destination for paddle boarding, kayaking, and swimming. It even has a separate beach where dogs can enjoy the water. But the lake is off-limits this week after city officials sampled the water and found concerning levels of blue-green algae, which can contain toxins harmful to humans, pets, and wildlife.

“Three of the last four years, we’ve ended up with blue-green algae in the lake,” Eric Lucas, the town of Windsor’s public service director, told a local media outlet. “It’s always present, but when it really takes off in this heat we’re having, that’s when it becomes a true hazard.”

Lucas is not alone in his discovery. Across the country, state officials are testing rivers, lakes, and coastal areas for evidence of cyanobacteria, the scientific name for blue-green algae. Florida’s Lake Okeechobee, with nearly half its surface already covered in a bloom, is on track to match its 2020 and 2021 levels. Kansas officials have listed nearly 20 local waterways with bloom warnings or watches; two Boston-based conservation groups are suing the EPA for failing to control pollution that has led to blooms in the Charles River; and North Carolina officials recently reported that several dogs have died after coming into contact with a toxic bloom on a lake south of Chapel Hill.

The pea soup-like sludge isn’t always toxic, but the longer it’s around, the more likely it will become toxic, producing a compound called microcystin that can kill pets and cause liver damage in humans. A 2021 CDC report tallied 321 emergency room visits by people who had come in contact with hazardous algal blooms between 2017 and 2019, presenting with respiratory, gastrointestinal, neurologic, and skin problems.

Farm fertilizer, manure, and other nitrogen- and phosphorous-containing contaminants that wash into water bodies drive the growth of blue-green algae. Climate change is predicted to make these blooms worse, as higher water temperatures prevent layers of water from mixing, which allows algae to grow faster. Surface-floating algae also absorb sunlight, which further warms the water and promotes even more blooms.

The EPA estimates that about 15,000 water bodies across the country are nutrient-impaired and therefore vulnerable to blooms, which wax and wane in size throughout the summer and can smell like rotten eggs, a factor that can drive tourists from recreation areas, affecting local economies. No federal agency currently tracks algal blooms, but the nonprofit Environmental Working Group produces an interactive map based on news stories and other sources. So far, this year’s map shows scores of blooms in Kansas, Florida, California, the Northeast, and the Rust Belt.

Predicting blooms is tricky. The National Oceanic and Atmospheric Administration (NOAA) uses satellite photos to forecast algal blooms, but that method works only for large bodies of water, like Lake Erie and Lake Okeechobee. “There’s a real limit to what you can detect from space when you get down to smaller water body systems,” says Ted Harris, who focuses on freshwater ecosystems at the University of Kansas.

Harris studies algal blooms across his state but concentrates on its largest water body, Lake Milford, a reservoir in the Flint Hills, about 90 miles west of Topeka. Harris found that blooms on the lake began to grow exponentially starting in the early 2000s, with a bloom covering the entire lake for the first time in 2011. That year, concentrations of microcystin were 7,500 times above what the World Health Organization considers safe. “It was one of the most toxic blooms that I’ve ever seen, globally,” Harris says. The lake has not seen that level of toxicity since, though it continues to experience large annual blooms.

Both Harris and Gail Hesse,​ director of the National Wildlife Federation’s Great Lakes Water Program, say that wind plays a big part in whether humans will be directly affected by algal blooms. If cyanobacteria growth occurs far from shore, it may not affect local beaches or marinas. But the wind can push a bloom into those areas, spurring health officials to close them.

Rainfall also plays a role. Ohio had lower than normal rainfall this spring, so fewer nutrients ran off farms into the Maumee River, which drains into western Lake Erie. The lake’s algal bloom is expected to be a bit smaller than average this year. “If it’s a really wet spring,” Hesse says, “we’re going to have a big bloom. If it’s a dry year, it’s going to be smaller.”

Still, says Donald Scavia, professor emeritus of environment and sustainability at the University of Michigan, “Whether [a bloom] is going to be bigger or smaller than the average is not the point. The average is not acceptable.” He notes that the federal government spent $30 billion between 2005 and 2015 to convince farmers to use practices that keep nutrients out of waterways, and that it plans to spend $60 billion more between 2019 and 2028. “It’s not working,” he says.

He and Donald Boesch, an emeritus professor of marine science at the University of Maryland, are promoting a new solution developed by a group of economists: have government scientists set limits on the total amount of nutrients that can enter a watershed; let farmers decide how to meet that limit based on what kinds of actions work best for their specific soils and climate; and then pay them for meeting the goal.

Scavia and Boesch have reached out to both the head of NOAA and the White House Office of Science and Technology Policy to discuss the idea. Scavia says, “We’re trying to get more people thinking about this idea.”