The Big Sioux River is covered with foam because the churning ice particles mixed with chemicals in the water. Witnesses tell ksfy.com the boy was looking at the river when he slipped and fell in around 6 p.m. Thursday.
Two men grabbed the boy, but then disappeared under the foam. Sioux Falls, South Dakota police searched the river for the men overnight, but they are believed to be trapped in the foam.
"We had him, though we had him. There were three of us that had him and he had a kid, the kid, he had the kid with him, but he just slipped, man, he just slipped," Napolean Ducheneaus, witness, said.
The men are presumed dead, according to published reports.