Nearly 100 beaches across the country are closed or under swimming advisories

Officials in at least 10 states have closed beaches or warned people not to swim in the water because of high bacteria levels ahead of the July 4 holiday.

Some closures are linked to bacteria from fecal waste, while others are due to high levels of cyanobacteria, also known as blue-green algae, in fresh water.

Florida, Illinois, Michigan, New Jersey and New York all reported dangerous levels of fecal waste at some beaches last week. Illinois issued advisories for 16 beaches, and Michigan announced two beach closures and five swimming advisories.

In Vermont, six locations are on high alert due to excessive cyanobacteria, and the state is asking people not to swim there.

Many beaches in the United States close each year due to harmful levels of bacteria. Environment America, an environmental research and policy center, found that more than half of the beaches tested had at least one day with dangerous levels of fecal contamination in 2022, according to Environmental Protection Agency standards.

Swimming in bacteria-rich waters can cause gastrointestinal illnesses and skin infections, especially in children, the elderly and people with weakened immune systems.

Research suggests that cyanobacterial algal blooms are more common due to climate change and that exposure to these algae can lead to lifelong health problems. Cyanobacteria produce microcystin, a toxin that can damage the kidneys, liver, or reproductive system if consumed in large amounts.

On Friday, Iowa found elevated levels of microcystin at two beaches and elevated levels of E. coli at five others.

In Massachusetts, 34 beaches have been closed, mostly due to high levels of E. coli or enterococci, types of bacteria that signal the presence of fecal waste. Enterococcus is detected in both seawater and freshwater, while E. coli is detected only in freshwater.

Robert Goldstein, commissioner of the Massachusetts Department of Public Health, said spikes in bacteria levels are common in the state after heavy rains. Rainwater picks up bacteria from the environment, such as animal or human feces, and then carries them into bodies of water.

“After the heavy rains we’ve had here in the Northeast over the last couple of weeks, the number of beaches that have to be closed is increasing,” Goldstein said.

About 5% of Massachusetts beaches are closed for the entire season, Goldstein said. The current closures represent a small fraction of the state’s 1,100 public and semi-public beaches, he added.

The Florida Department of Health also determined that several beaches in Monroe and Hillsborough counties have poor water quality due to high levels of enterococci.

In San Diego, three beaches have been closed and two have been issued warnings due to dangerous bacteria levels. And in southeastern Virginia, several sites are under similar notices.

Goldstein said bacteria levels can change frequently, so people should check their health department’s website for the latest updates on where it’s safe to swim and stay on top of beach safety warnings.

People can also take steps to reduce the amount of bacteria they add to the environment. Goldstein suggested that beachgoers pick up after their pets and dispose of their waste properly, which can help limit the amount of pet waste entering the water.

“Whatever bacteria they introduce into the environment, it’s likely that after heavy rains those bacteria end up in the bodies of water around us,” he said.