Outbreaks of potentially toxic algae are fouling lakes, rivers and other bodies of water across the U.S. Nationally, news reports of algae outbreaks have been on the rise since 2010.

What’s worse, some algae blooms produce dangerous toxins called microcystins. EWG just released a report showing that microcystins have been found in lakes across the U.S. – even when there’s no visible toxic algae outbreak.

Here’s what you should know about kids’ and pets’ safety around potentially dangerous water and what you can do to prevent the growth of algae blooms.

What are algae blooms?

These smelly blooms aren’t actually algae at all, but photosynthetic microorganisms called cyanobacteria.

Runoff from farm fields is often polluted with phosphorous and other chemicals in manure and commercial fertilizers. When this polluted runoff gets into lakes, it feeds the growth of cyanobacteria, especially in warm weather. Increasingly heavy rains and flooding, exacerbated by the climate crisis, make the problem worse.  

What are microcystins?

Many algae blooms are gross, forming a foul-smelling slime on a lake’s surface, ­but not hazardous. But for reasons no one yet understands, some produce poisonous chemicals called cyanotoxins, including the group known as microcystins.

What are the health risks?

Microcystin-producing cyanobacteria are a hazard to anyone, but the Centers for Disease Control and Prevention says children are especially vulnerable, since they’re most likely to ingest water while swimming. Exposure can cause coughing, nausea, weakness, cramping and headaches, as well as long-term health effects such as liver failure.

Contact with skin, drinking contaminated tap water or eating contaminated fish can also cause health problems. Even breathing in microcystins can be harmful, and recent studies have shown that the toxins can become airborne, drifting a mile or more from the site of the outbreak. 

How can I recognize and avoid algae blooms?

The best approach is to check with your city, county or state health departments, which may issue warnings. You can also use EWG’s map to see whether authorities have found microcystins in a particular lake in the past few years.

If you can’t find information about a specific lake, get to know the warning signs. Look out for dead fish or animals in or near the water, and slime that looks like blue, blue-green, bright green or dark green spilled paint.

Only experts who test the water can determine definitively whether an algae bloom is toxic. So if you come across what looks like an algae outbreak, stay away – even if you’re not sure it’s toxic. Don’t swim in it, and do your best to avoid breathing the air around it. Contact your health department and alert local news media.

What should I do if I think my child has been exposed to a toxic algae outbreak?

If you think your child has come into contact with toxic algae, or shows flu-like symptoms after playing in or near it, rinse them off with water. Make sure they also drink plenty of water. Seek medical attention as soon as possible.

How can we prevent algae blooms?

Farming practices like vegetative buffers along streams and rivers help minimize runoff, but these practices won’t be widely implemented without regulations that require farmers to apply them.  

Ideally, states would test lakes and other bodies of water for microcystins and other cyanotoxins and warn the public when there’s danger. But EWG’s new report found that only 20 states test regularly for microcystins and make the data public, and often only after a delay.

The Environmental Protection Agency should regulate these toxins to protect our tap water supplies. More than two-thirds of all Americans get their drinking water from utilities that rely at least in part on lakes, rivers or other surface water. Yet the EPA doesn’t regulate the level of microcystins and other cyanotoxins in drinking water.

For more info about toxic algae outbreaks, check out this overview. EWG also maintains a resource center on algae blooms here.