CDC Alert: People and Animals Are Increasingly Getting Ill From Toxic Algae
CDC Alert: People and Animals Are Increasingly Getting Ill From Toxic Algae

By Jack Phillips

A report from the U.S. Centers for Disease Control and Prevention (CDC) found that more people and animals are getting sick from toxic algae that forms in bodies of water across the United States.

The report found that some animals—but no people—have died from the effects of toxic algae. Some 16 states reported a total of 117 illnesses among people and at least 2,715 animal illnesses as a result of harmful algal bloom (HAB) events, said the agency in a report published this week.

The vast majority, or 90 percent, of toxic algae blooms occurred in fresh water, namely in reservoirs, impoundments, and lakes, according to the CDC. Based on 2021 data, some 368 harmful algae bloom events were reported, representing a major increase compared to previous years, as fewer than than 250 HAB events were reported in 2020 and 2019, it found.

The blooms occurred in Arizona, California, Illinois, Kansas, Michigan, Minnesota, North Carolina, Ohio, Oregon, Pennsylvania, Tennessee, Utah, Virginia, Washington, Wisconsin, and Wyoming. But Michigan and Pennsylvania saw the most, with 77 each, and Utah saw the most illnesses among people, the agency said.

Washington state saw the most animal sicknesses. In one instance, an algae bloom killed off 2,000 bats in the state, according to the CDC.

An aerial photo shows blue-green algae enveloping an area along the St. Lucie River in Stuart, Fla., on June 29, 2016. (Greg Lovett/The Palm Beach Post via AP)

“HAB events of public health concern are primarily caused by microalgae (e.g., diatoms and dinoflagellates), cyanobacteria, and the toxins they can produce,” the CDC wrote. “HAB events, which can be intensified by factors such as nutrient pollution and warmer water temperature, can have public health, environmental, and economic impacts.”

The algae bloom events generally peak in August, the report found, and about 90 percent occur in lakes, reservoirs, and impoundments, as well as other fresh water. The blooms emerge from the rapid growth of cyanobacteria or algae known as blue-green algae, the agency said.

These algae blooms are different than red tide events like the ones that impact Florida’s coastal waters. For red tide, it’s formed by the bacteria Karenia brevis, which can make the water appear brownish-red.

Human illnesses occurred primarily in June, it said, noting the most commonly reported symptoms and signs were gastrointestinal problems, fever, headache, and dermatologic. Animals got sick mainly in August, the CDC report also found, and it mostly involved wildlife.


Over the years, local officials in a number of states have issued advisories or even warnings about toxic algae in waterways. The toxic algae has also been found in Florida waterways for years as it thrives on excess phosphorus and nitrogen from fertilizers, sewage, and septic tanks.

A large algae bloom is blossoming across Florida’s Lake Okeechobee this week, leading to health warnings and the closure of a local marina. The bloom is believed to be about 440 square miles and can be seen from space, according to images posted by NASA.

Last week, health officials in Kansas confirmed that nine of its lakes were impacted by blue-green algae and sent out several advisories. In Maryland this week, officials in Montgomery County said that people who may have ingested water in the Triadelphia Reservoir should contact the local health department.

The reason why is high levels of toxic algae and HABs were found in the reservoir, Montgomery County officials said.

The City of Toledo water intake crib is surrounded by algae, Sunday, Aug. 3, 2014, in Lake Erie, about 2.5 miles off the shore of Curtice, Ohio. (AP Photo/Haraz N. Ghanbari)

The New Hampshire Department of Environmental Services in June 2022 said it detected high concentrations of cyanobacteria at Mascoma Lake and Goose Pond. The department had advised visitors to avoid contact with the water and to keep pets away.

In Vermont, officials in 2019 issued alerts about the algal blooms being found in Mallets and Missisquoi bays in Lake Champlain at the time. They said at the time that dogs are especially vulnerable to the toxic effects.

Scientists believe a combination of factors can trigger large blooms, including summer temperatures, slow water circulation, and excessive nutrients, especially nitrogen and phosphorus. And some blooms generate toxins such as microcystin, which can cause nausea, fever, and liver damage in humans and can kill animals.

The Associated Press contributed to this report.

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