Normally a good place to cool off in the summer, northern New England rivers are anything but these days — raging and dangerously swollen from heavy rains.

In the past two weeks, at least four people have been swept off their feet in New Hampshire rivers, three dragged down by the swift current and drowned.

“We’ re at spring levels and people are underestimating the strength of the current,” New Hampshire Fish and Game Maj. Tim Acerno said Tuesday.

He commented as Fish and Game officers reported finding the body of a Massachusetts man who slipped into the Swift River on Sunday. On July 25, a Texas teen drowned in the east branch of the Pemigewasset River. On July 29, a Merrimack woman slipped and fell into the Souhegan River. Her body was recovered late Saturday.

Also on Tuesday, a man was swept downstream in the Merrimack River in Manchester, but made it to shore.

“Knock on wood, we haven’ t had a really serious event of that sort” where people died in swollen rivers, said Vermont state police Lt. Dan Begiebing. “But rivers hide hidden dangers — currents, eddies, underwater debris — and you have the potential to drown.”

Acerno is cautioning people to stick to roped-off swimming areas. The rivers are too high and the currents too fast to be trusted, he said.

People wanting to cool off are stepping onto rocks made slippery by algae that grow thick in the summer, he said.

Some who slip don’ t resurface and their bodies aren’ t found for hours or days later and miles downstream.

That was the case of the Texas teenager who was spending the summer working for the Papermill Theatre in Lincoln. He was swept off some rocks and drowned. His body was found about five hours and three miles downstream that night.

Acerno said the river levels also are rising and falling swiftly with the torrential rains that have fallen on the region. That can mean a river swollen and raging one day can be several feet lower within 48 hours, he said.

That was the case on Sunday when David Hildebrandt, 29, of Boston slipped off a rock and was swept away in the Swift River in Albany. By Monday morning, the water had dropped two feet, said Acerno.

On Tuesday, it had dropped again. Hildebrandt’ s body was found late Tuesday morning.

Acerno said there’ s no one area where rivers are more dangerous.

“It’ s statewide. It’ s dangerous because of the slippery conditions and strength of the current,” he said.

The same is true in parts of Vermont and Maine.

In Fair Haven, Vt., Police Chief William Humphries said Tuesday he may approach the Selectboard about posting no-swimming signs at a popular spot along the Castleton River until its level recedes.

The comment came a day after three girls had to be rescued when they were swept downstream by high water on Monday.

Lisa Dufield, 17, was swimming with her sisters Sara 14, and Antonia, 10, when they were swept downstream. They were able to grab onto a slate wall along the river’ s edge less than 50 yards above a series of dams and waterfalls, the chief said.

“If they had gone another 25 or 30 yards, I don’ t know what would have happened,” Humphries said.

Rescuers slid a ladder down the slate wall to allow the girls to climb out.

Linda Dufield, the girls’ mother, said her eldest daughter grabbed the 14-year-old, who is autistic, and held onto her for several minutes, yelling until help arrived. “My daughter’ s the big hero, my daughter Lisa,” Dufield said.

In Maine, high water has caused problems for canoeists along the Saco River in Fryeburg, where five canoes capsized Sunday evening. Ten people were thrown into the water and one was thought to be missing but later was found. Two canoes with four people capsized Friday.

Ann Perante, administrative assistant at the Fryeburg Police Department, said the recent high water has swept away the canoes of people who camp along the banks of the Saco, leaving the canoeists stranded.

Wet weather does not appear to be drying up anytime soon.

Maine has more than made up for a dry spring, with higher than average rainfall this summer. Portland got 4.7 inches in July, which normally gets 3.3 inches. Rainfall records were set on two days last month.

August is looking to be another wet month, with 2.8 inches recorded on Sunday. Portland normally gets 3 inches for the entire month.

In New Hampshire, the National Weather Service rainfall total for Concord in July was 6.48 inches, almost twice the normal amount of 3.37 inches.

On Sunday, a record for Aug. 3 was set in Concord when 1.09 inches fell. The old record for the date was 0.9 inches set in 1932.

Associated Press writers

Dave Gram in Montpelier and Jerry Harkavy in Portland contributed to this report.