This latest threat to summer fun has forced a handful of states to close local beaches because of heavy contamination.

By Anthea Levi
July 06, 2017
2016 Getty Images
Joe Raedle/Getty Images

For many people, summer means heading to a local lake and cooling off with a swim. But recent outbreaks of toxic algae in lakes and ponds across the country have shut down some of these swimming spots, leaving the water surface coated in green and posing a threaten to human and animal health.

Last week, two Northern California dogs died after swimming in lakes that contained harmful algal blooms (or HABs). Earlier this summer, confirmed cases of HABs prevented visitors to Washington’s Anderson Lake State Park from enjoying the water. New York, Florida, and North Carolina have also reported HABs in bodies of water as well.

Of course, not all algae are dangerous. Some types help produce oxygen, making them crucial for wildlife that lives underwater. But HABs are overgrowths of algae that can occur both in fresh or saltwater environments. The blooms produce toxins that are poisonous to humans and animals, as well as the ecosystems they inhabit.

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“HABs can be an irritant to the skin, depending on how you react to the organism,” says Marit Larson, chief of natural resources in the New York City Department of Parks & Recreation. “But they can also produce nausea or more extensive gastrointestinal symptoms,” such as vomiting. Ingesting HABs—say, by swallowing water while swimming in a lake where it thrivesmay even trigger neurological effects.

“That said, people don’t usually ingest a lot of water, especially in areas where it doesn’t look appealing to swim,” adds Larson. The greater concern is for animals, including pets, since they're more likely to go in or drink from algae-heavy water.

So why is toxic algae making headlines now? HABs grow best in warm, nutrient-rich environments that attract agricultural or lawn runoff, says Larson. Rising temperatures triggered by climate change may also play a role. “Temperatures are warming and seasons are extending longer, which makes us see these blooms way later into the fall and way earlier in the winter,” explains Larson. “And since climate change is increasing the potential risk of HABs, we’re paying more attention to them now.”

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The best thing you can do to protect yourself is to steer clear of it. That means knowing what to look for next time you're planning to take a dip in a local watering hole or let your dogs go for a run beside a pond. Unlike benign algae that tends to resemble plants, HABs are generally bright green. They spread across the surface of the water rather than become clumpy or stringy, says Larson.

As long as you (and your pet!) don't swim or splash around in areas that appear to contain HABs (or are confirmed to have them), there’s no reason to panic. If you do have direct contact with this green goop, just wash your hands as soon as possible.