There’s nothing quite like a day at the beach to beat the heat, but one Massachusetts mother learned that even the refreshing ocean can hold unexpected dangers—ones that might not cross your mind on a hot summer day.

Heather Cassini, 40, visited Hampton Beach in New Hampshire with her family on July 4. Like many families enjoying the holiday, they were soaking in the sun, cooling off in the waves, and spending quality time together. But what started as a fun outing took a frightening turn when her 10-year-old son, Declan, suddenly said he wasn’t feeling well.

Initially, Cassini didn’t think much of it. It was a hot day, and Declan had been playing hard in the ocean.

“I thought the breakfast was just too much for the waves and he just needed to lay down,” she later shared in a now viral Facebook post. But as they made their way off the beach so Declan could rest, things escalated quickly. He became disoriented and collapsed onto a nearby sunbather. Though he managed to stand up briefly, he fell again.

“I’m pregnant and frantically trying to pick him up,” Cassini told Today.com. “He’s going in and out of consciousness and vomiting. And he was so pale.”

Thankfully, several nearby beachgoers witnessed the commotion and rushed over to help. Among them were several nurses who immediately assessed the situation and stayed by Declan’s side while paramedics were called. They worked to keep him conscious, stable, and warm.

“God bless all the people around us. There were so many nurses,” Cassini said, still clearly shaken. “After what felt like eternity he was up and talking. We waited for him to feel better and got him to the car.”

Eventually, it was determined that Declan had developed hypothermia—despite the warm air temperatures. The ocean water that day was around 52 degrees, and after prolonged exposure, his body began to shut down.

“I had no idea that this could happen,” Cassini said. “You think about sunburns and dehydration and all the things that can happen in the water, but I never considered cold shock.”

Now that Declan has fully recovered, Cassini wants to spread the word. She’s urging other parents to be aware of how cold water—even in summer—can pose serious risks, especially for children who may not recognize when their bodies are approaching danger.

“Just a warning to those with kids who feel no cold and love the water. Just because they can handle it doesn’t mean they can handle it.”

Many people don’t realize that hypothermia doesn’t only occur during cold weather or winter activities. It can sneak up in summer too, particularly when cold water temperatures are involved.

This experience is a critical reminder to pay attention to more than just the sun on a hot day. Share this story with others—it could help someone else recognize the signs before it’s too late.