On a rainy Sunday in July, the Trailblazers began to arrive at Camp Squanto, a 100-acre sleep-away retreat in southern New Hampshire. Parents drove them.

Made up of children about to enter grades four through six, the Trailblazers were looking forward to summer days spent playing sports, doing arts and crafts projects and jumping from floating docks into the chilly waters of Swanzey Lake.

As many of the campers tried to settle in, the rainstorm grew more intense. Within hours, flash floods turned the roads around the camp into muddy rivers.

Campers, parents and staff members huddled in the dining lodge. Many of them bedded down on the floor for the night, intermittently checking weather updates as the rain continued into the next day.

The next afternoon, the local Fire Department carried out an evacuation. Camp Squanto was closed.

“We’ve had heavy rain and things like that,” Jim Condap, the camp’s executive director, said in a phone interview. “But nothing of this magnitude. Never.”

The deluge that wiped out the session at Camp Squanto, a Christian youth camp that is part of Pilgrim Pines Camp and Retreat Center in Swanzey, N.H., occurred during a summer of extreme weather events across the United States, many of which have been fueled by climate change.

In addition to torrential rains and deadly heat waves, wafts of smoke arising from the nearly 900 wildfires in Canada have darkened the skies in much of the country and made the air dangerous to breathe.

Campers are still swimming, playing tetherball and singing around the fire as they take steps toward independence this summer, but they have also been contending with a precarious natural environment.

Parents who sent their kids off for an enriching experience in the great outdoors — perhaps with the hope of getting some child-free time — have received unsettling messages from camp directors, with updates on the latest flood, influx of unhealthy air or blast of heat. The wild weather has come at a time when the demand for summer camp is up, three years after the start of the pandemic.

It started with the smoke drifting down from Canada, which prompted air quality alerts in the Midwest and Northeast as camp season was getting underway.

At Tanglewood Nature Center in Elmira, N.Y., which runs a day camp for children of elementary school age, the Air Quality Index hit 183 this month, an unhealthy level. The smoke forced the campers to stay indoors, where they built papier-mâché volcanoes. Wildfire smoke also meant more indoor activities for campers at Y.M.C.A. Camp Kon-O-Kwee Spencer in Fombell, Pa.

The storm that wreaked havoc on Camp Squanto, which dumped up to eight inches of rain across much of the Northeast, also disrupted Camp Killooleet in Hancock, Vt. Washed-out roads led to the cancellation of a three-day camping excursion in the Green Mountains that had been planned for 80 campers. Efforts to find an alternate location for an overnight trip didn’t pan out.

“A lot of places were soggy,” said Kate Seeger, who runs the nearly century-old camp with her husband, Dean Spencer. “Friends said, ‘You’re welcome to come, but there’s no place to pitch a tent.’”

At Windridge Tennis & Sports Camps, in Roxbury, Vt., thunderstorms have kept the 110 children off the red clay courts too often in recent weeks, said Nifer Hoehn, a camp co-director.

“This summer has been extremely hot and humid for Vermont,” Ms. Hoehn said. “We’ve had our kids inside more than normal, which we don’t love. When they’re outside, because of that humidity, it’s uncomfortable.”

Summer camps in the West and Southwest have tried to hold steady through bouts of punishing heat. At Heart O’ the Hills, an overnight camp for girls 6 to 16 in Hunt, Texas, hot weather has long been a concern. Since last month, a heat dome has kept temperatures above 100 degrees in many parts of the state.

“We have a giant cooler — we call it the Monster — where the girls can always access water,” Cindy Janke, the camp’s office manager, said. “They always take a break between 2 and 4 to get out of the heat. At mealtime, we had them drink two glasses of water instead of one.”

Such precautions are not unknown at the decades-old camp in the Texas Hill Country. But this summer, the counselors are being especially careful.

“We’re more on top of it because of the extreme heat,” Ms. Janke said. “It’s been over 100 here. The girls are asked — and the head staff constantly check to make sure — that they have a water bottle wherever they go.”

Camp directors have considerable experience in planning around weather events, said Tom Rosenberg, the president and chief executive of the American Camp Association, an accrediting organization for summer camps. “That planning is getting stronger,” he said, “because we’ve been tested in ways we haven’t before.”

And the summer of 2023 has taught campers to be resilient and adaptable.

“Part of the camp experience is about learning to take care of yourself,” Mr. Rosenberg said. “Part of that is teaching them how to have fun in spite of the weather. This generation of kids are growing up knowing that everybody brings a hat, a water bottle and sunscreen to camp.”

In Phoenix, the temperature was above 110 degrees for 19 days straight, breaking a record. A two-hour drive away, at Friendly Pines Camp, in Prescott, Ariz., the days have been slightly cooler — in the upper 90s, topping out at 100.

For the 230 kids in the camp’s current session, those temperatures have been a welcome relief, said Sayaka Pierson, the business manager at Friendly Pines.

“They’re actually doing great, because most of them come from Phoenix,” Ms. Pierson said. “Phoenix is 116, 120. They’re saying, ‘This seems cool.’”

Heat waves and related natural disasters have also affected campers outside the United States. The BBC on Monday reported that 1,200 children were evacuated from a summer camp in Loutraki, Greece, a seaside town west of Athens, as wildfire flames approached. Two other summer camps in Greece were evacuated because of the fires, which have come during a run of searing days across southern Europe.

For many children, the weather-related disruptions have been a letdown. Silas Johnson, 9, was all set to attend Camp Squanto this month — the first time he was going to spend a full week there. His mother, Sarah Cowan Johnson, was driving him from Rhode Island to New Hampshire when the storm hit. As they drew close to the camp, they hit a roadblock and were turned away by police.

“There was a loud, vocal expression from the back seat,” Ms. Cowan Johnson said.

Her son had been looking forward to archery, swimming and kayaking, she added. He ended up at home for the week he would have spent at camp.

“He’s been reading ‘Calvin and Hobbes,’” Ms. Cowan Johnson said. “He did Parkour. He had to think of things to do.”

Audio produced by Tally Abecassis.