CDC Warns Public to Avoid the Toxic Algae “Blooming” in Warming Waters

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Toledo, Ohio is breathing a sigh of relief after the National Oceanic and Atmospheric Administration announced on Thursday that the annual toxic algae bloom in Lake Erie’s western basin is forecast to be “smaller-than-average” compared to recent years. In 2014, an explosion of cyanobacteria sent officials scrambling and forced the water treatment plant to shut off the city’s tap water for three days. That wasn’t even the largest bloom on record in western Lake Erie. Levels of cyanobacteria in 2011 and 2015 were even higher, creating a thick layer of blue-green scum on the lake.

Cyanobacteria produces toxins that can harm the internal organs of humans and wildlife. Symptoms of exposure include headache, pain, dizziness, vomiting and diarrhea. The Great Lakes region enjoys one of the world’s largest supplies of fresh water, and residents were shocked by the water shutoff, not to mention the signs posted at beaches to warn swimmers the lake was poisonous. Local activists sprang into action, organizing a ballot initiative to save the lake.

Harmful algae blooms, as researchers call them, are not just Lake Erie’s problem. Nearly every state is impacted by the toxic blooms, which threaten wildlife, vital economic resources and public health, according to the U.S. National Office for Harmful Algal Blooms. In 2018, a toxic bloom in Oregon’s Detroit Lake reportedly caused panic in Salem, and now both Oregon and Ohio require water utilities to test for algae toxins. More states could soon follow suit. Researchers are now studying harmful blooms in the Chukchi Sea, a remote sea in the Arctic Ocean, which was once thought to be too cold to support toxic algae. Indigenous fishers harvest the same waters for food. Scientists say there are multiple causes of algae blooms, but heavier rains and warmer waters associated with climate change are combining with water pollution to exacerbate the problem.

The Centers for Disease Control recently released a nationwide advisory urging people to avoid “toxic algae and cyanobacteria” that can quickly grow “out of control” in freshwater lakes and rivers, coastal saltwater areas, and brackish bays and estuaries across the country. Harmful blooms often look like “mats” of “scum” across the water, and can make the water appear different colors, such green, red, brown and blue.

After a campaign by activists, Toledo voters approved a plan to give Lake Erie the legal right to defend itself in court, a temporary victory for the “rights of nature” movement. However, the plan was thrown out by a federal judge in 2020. Toxic algae blooms remain a topic of discussion at dinner tables across the Great Lakes region today, especially during the summer, when people head to the beach and the blooms appear. Plenty of algae occur naturally and are not toxic, but the shallow, western basin of Lake Erie has been dominated by the harmful cyanobacteria in summers past.

Scientists point to several explanations for toxic algae blooms. Heavy summer rains push polluting runoff from industry, cities and industrial agriculture directly into rivers and streams, which carry the contamination into lakes, bays and coastal areas. This runoff can contain excessive levels of nitrogen and phosphorus, often from fertilizer. As waters warm in the summer, these nutrients feed large blooms of algae, which can suck the oxygen out of the water and endanger fish and other wildlife even if they do not release toxins.

With rainfall and warm summer weather being crucial factors in the algae bloom equation, climate change has quickly become a topic of interest for algae researchers. Researchers now say global warming is making algae blooms worse in certain regions of the world and particularly in large lakes. One 2019 study used satellite imaging to estimate that two-thirds of 71 large lakes across 33 countries saw algae bloom intensity increase over the past three decades. Researchers caution that there are also far more local causes of algae blooms, including weather patterns, naturally occurring nutrients and agricultural practices, but global warming is not helping.

Don Anderson, director of the U.S. algae bloom office at the Woods Hole Oceanographic Institution, is one of the nation’s top experts on harmful saltwater algae. Anderson has studied blooms from Maine to Florida, but the biggest climate story is coming out of Alaska, where blooms of the Alexandrium cantanella are appearing in the Chukchi Sea. Scientists previously thought the sea was too cold for the organism to germinate and reproduce in the Chukchi Sea, but warmer temperatures and melting sea ice are making the water much more hospitable to huge blooms of the toxic algae.

“The same organism that we study and have studied for decades in the Gulf of Maine and other parts of the U.S. — we thought for a long time that the waters were too cold up there for it to do very well,” Anderson said in an interview.

In a recent study published in the Proceedings of the National Academy of Sciences, Anderson and his team found conditions ripe for large, recurrent harmful algae blooms in the Chukchi Sea. A. cantanella grows from “cysts” that act like underwater seed pods, which drift from warmer waters to the south and become embedded in layers of sediment in the sea floor. The concentration of cysts in a “bed” below the Chukchi is among the highest in the world for this species, the study found, and the bed itself is at least six times larger than any other. Poisonous blooms have threatened public health in southeastern Alaska for centuries, but now a region that was once immune is poised to support annual blooms on a “massive scale.”

“It’s a big story because the people up in that area, local Indigenous people, are subsistence harvesters: They live off the ocean, from seabirds to sea lions to walrus to whales to all these different marine animals that virtually all can be vectors for these poisons,” Anderson said.

Anderson said no one in western Alaska has yet reported becoming sick after harvesting from the Chukchi Sea, and scientists are still working to understand how the algae’s biotoxins work their way through the food chain beyond shellfish. A. cantanella poisons shellfish worldwide, and in many places, shellfish harvested for food are tested for algae toxins. However, in the remote and tribal regions on the Chukchi Sea, testing the day’s catch for algae toxins and monitoring the water for blooms has never been part of the harvesting process. For Indigenous fishers there, toxic algae are now part of a new climate reality.

People who experience symptoms and believe they have been exposed to toxic algae should call their doctor or a poison control center, the CDC says.