What you need to know
- Dangerous waterborne organisms are becoming more widespread because of climate change.
- Rising temperatures allow flesh-eating bacteria that once lived primarily in the Gulf Coast to move farther north each year while also fueling the growth of toxic algae that threaten humans and animals.
- You can stay safe by avoiding water if you have cuts or scraps—or if the water is dirty or foul-smelling—and washing your skin as soon as you get out of the water.
This summer, several states reported dangerous bacteria and algae in lakes, rivers, and coastal areas that made people and animals seriously ill. Due to climate change, warming water temperatures create an ideal environment for potentially deadly waterborne organisms to flourish.
Flesh-eating bacteria are moving into new regions
In 2023, the Centers for Disease Control and Prevention warned about unusual but severe infections of bacteria called Vibrio vulnificus. The microbe lives in warm salt or brackish (mixed salt and fresh) water, and it can infect open wounds, killing skin, muscles, and nerve cells. Around one in five infections are fatal, and many require amputation.
For years, most U.S. cases happened along the Gulf Coast. Now, infections are rising farther north as coastal waters warm. A 2023 study found that infections in the Eastern U.S. increased eightfold between 1988 and 2018, and the bacteria’s range moved roughly 30 miles north each year.
“Vibrios generally grow well between 15 and 40 degrees Celsius [59-104 degrees Fahrenheit], so as the temperature warms, their generation time shortens and they divide faster and faster,” said Rita Colwell, a microbiologist at the University of Maryland who has studied Vibrio for over 50 years, in a 2023 interview.
Warming waters fuel an explosion of toxic algae
Algae naturally grow in lakes and ponds, usually in small amounts. But when conditions are right, algal blooms can grow fast, forming a foamy or slimy substance that floats on the water’s surface.
Some harmful algal blooms release toxins that are dangerous to humans, pets, and wildlife. Touching, inhaling, or swallowing water containing these toxins or eating seafood that live in affected waters can cause vomiting, diarrhea, and liver damage.
Warm water and heavy rainfall make these blooms more likely, and both are becoming more common with climate change. Pollution from farms, lawns, and cities feeds algae, and harmful blooms are becoming more frequent and more intense.
“If you have a longer summer, then you’re going to have more time for these algae to continue to grow, and grow larger and be able to go into things like our sources of drinking water, or into a lake that people like to fish in or play in,” said Mae Wu, a former deputy assistant administrator at the Environmental Protection Agency, in a 2024 interview.
How to stay safe
You can lower your risk with a few simple steps:
- Avoid salt and brackish water if you have open cuts, scrapes, or recent piercings or tattoos. If you do enter the water, cover any wounds with waterproof bandages.
- Avoid water that is discolored, slimy, or foul-smelling.
- Wash your skin with soap and water immediately after getting out of the water.
- Cook all seafood well, and wash your hands and surfaces after handling raw seafood.
- Check local health advisories before swimming or fishing.
- If you notice symptoms of a vibrio infection or harmful algal bloom, contact a health care provider immediately.