Five people died in the Scioto River in central Ohio after one of them went in for a swim on Sunday and began struggling and others tried to rescue the person, the authorities said.

The group had gathered by the river near the O’Shaughnessy Reservoir, just northwest of Columbus, to enjoy a summer evening and to fish, the Delaware County sheriff, Jeffrey Balzer, said at a news conference on Monday.

At some point one person in the group decided to swim, and “that’s when the tragedy started to occur,” Sheriff Balzer said. That person started struggling in the water, he said, and two others went into the river to try to help. Then those two began to struggle, he said, prompting two more people to venture into the river.

At about 9 p.m., a driver noticed a young child who was “clearly distraught,” running alongside a road by the river, Sheriff Balzer said. The driver called 911 and reported that the child had said that his “family was in the river,” Sheriff Balzer said.

Firefighters, police officers and other emergency workers responded and found two adult women in the river; they were taken to hospitals and pronounced dead, Sheriff Balzer said.

Rescue crews continued searching the river until they found the bodies of the remaining three people, all adult men, at about 2 p.m. on Monday, Tracy Whited, a spokeswoman for the sheriff’s office, said in an email.

Sheriff Balzer said the child and another child who had been with the group were in the care of the county’s child welfare agency. The children are 6 and 7 years old.

It was not immediately clear how the people in the group were related, but Sheriff Balzer said: “There may have been two sets of parents, two children and then someone else.”

Ms. Whited said in an email that the sheriff’s office was investigating, but that “we’ve had a few challenges.”

“In addition to the children’s ages, there is the trauma as well as a slight language barrier,” she said. She did not say what language other than English the children spoke.

Sheriff Balzer said it did not appear that there was any strong undertow in that section of the river. He said the deaths were a reminder of the importance of being safe around water.

“There’s no shame in having a life jacket, or something like that, that saves people every day,” he said. “So just be cautious, be aware of your skills and whether or not you’re confident enough to be in the water.”