Starlight Park, a sliver of green hemmed in by railroad tracks and the Bronx River, is a popular hangout spot for local teenagers, though a sign by a dock there makes clear that swimming and diving are not allowed. The boys were with several friends at the park on Friday afternoon. The temperature was in the 80s and the sun was shining, and at some point they decided to go swimming, a Police Department spokesman said.

It was not immediately clear at what point the boys got into trouble or whether they knew how to swim.

Diaminique Mims, 15, a friend of the boys, said she was at a basketball court about 200 yards from the river on Friday when a group of friends ran up to her, frantic and asking if she could swim.

Miguel Perez, 14, who also was there, said that at first he thought it was a joke when the youths said two of their friends were in need of help. Then, he said, he saw that some were crying.

The group of teenagers ran to the bank of the river. At one point, they said, a boy named Gregory tried to lower himself in the water and reach the boys while still holding on to land. But they were too far away.