Seven US teenagers from two families were splashing around in the shallow waters of Louisiana's Red River when one of them stepped off a slippery ledge and plummeted into much deeper water.
The others tried to save the boy even though none of them could swim, but they too were swallowed by the water which was about six to nine metres deep.
Their relatives, who could not swim either, looked on helplessly as six struggling teens screamed for help, then vanished and drowned.
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Six dead ... family members react as authorities scour the water for bodies.
Six dead ... family members react as authorities scour the water for bodies. Photo: AP
DeKendrix Warner, 15, who was the first to fall in, was rescued by a bystander.
"I stepped and I started drowning," he said from his inner-city Shreveport home in a low voice, his eyes staring at the ground.
The large group of family and friends had gathered for an afternoon of swimming and barbecuing in the oppressive heat. The group had been at the river for only about 10 minutes when tragedy struck - they didn't even have time to set up the barbecue.
DeKendrix said he was kicking and felt as if the river was pulling him under. When he was finally pulled from the water, he told the man to go help his cousin.
Those who drowned were Takeitha Warner, 13, and her older brothers, JaMarcus, 14, and JaTavious, 17; and Litrelle Stewart, 18, LaDairus Stewart, 17, and Latevin Stewart, 15.
The area where the drowning occurred is not a designated recreational or swimming area but is often frequented by swimmers and boaters. There are no lifeguards on duty.
"The river is a dangerous place. It's no place to even put your foot in if you don't know how to swim," said Shreveport Fire Chief Brian Crawford.
Swimming skills can be scarce among African-Americans such as the teens in this tragedy. A study commissioned by the sports governing body USA Swimming found 69 per cent of black children had low or no swimming ability compared with 41.8 per cent of white children.
Segregation kept African-Americans out of public and private pools for decades and the disparity continues because many poor and working-class children have limited access to pools or instruction.
The study did not look into swimming ability based on rural versus urban environments.
The drowning "confirms that what we are finding, that this continuing cycle of people not knowing how to swim and their children not knowing how to swim and still being around water", said Sue Anderson, USA Swimming's director of programs and services. "It's the continuing lack of awareness of how important it is that children learn how to swim."
The federal government says African-Americans drown at a rate 20 per cent higher than white people. A lack of access to swimming pools and a lower interest in swimming skills are among the possible explanations, the Centres for Disease Control and Prevention said.
Marilyn Robinson, a friend of the families, told The Times of Shreveport she watched helplessly as the victims went under. She said a large group of family and friends, including roughly 20 children, were out at a sandbar to barbecue and have a good time. They frequent the area and were familiar with the water, she said.
DeKendrix said he had been going down to the river all week.
"None of us could swim," Ms Robinson said. "They were yelling 'Help me, help me. Somebody please help me.' It was nothing I could do but watch them drown one by one."
It took more than three hours to find all the bodies.