Emergency crews responded around 1 p.m. to the area near 63rd Street Beach on the city's South Side, police said.
The man, identified as James Hammond, and three children -- his niece, nephew and a young family friend -- were in a boat when the 11-year-old boy fell into the water, fire officials said. Hammond jumped into the lake to help the child, but went under.
The 11-year-old boy was in a donut that flipped over.
"As my nephew started to drift away, my brother hopped and as he was swimming towards him, a rip tide pulled him down and he took in water, a lot of water in the lungs, and drowned," Michael Hammond, the victim's brother, said.
Michael Hammond said his daughter called from the boat.
"She was saying that she couldn't see Uncle James no more, he was in the water," Hammond said. "She couldn't see Uncle James."
The boy, who was wearing a life jacket, was rescued by Chicago Park District lifeguards who rowed out to help, police said. Two children in the boat got the attention of the lifeguards by blowing whistles. They were all wearing life vests and were not hurt.
"Lifeguards on the beach heard the commotion and were able to quickly row out there in a lifeguard rowboat and assist the 11-year-old who was in the water," said Ron Dorneker, deputy district chief for the fire department.
A helicopter dive team pulled Hammond out of the water. He was unresponsive and taken to the University of Chicago Medical Center, where he was pronounced dead, officials said. The child was transported to Comer Children's Hospital in good condition.
Hammond owned the small powerboat, family said. He was raised on the city's West Side but was living on the northwest side with his wife.
Hayes Beach, also known as 63rd Street Beach, was closed Monday afternoon following the incident.
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