An investigator into the misfortune, which transpired close to Rotherham on 28 May last year, listened to how his friends had been provoking one another to dive into the icy water.
The friends then decided to play rock, paper scissors to reach a decision who would jump first, with Sam losing the bet, YorkshireLive reports.
The victim who had recently been diagnosed with autism and other complex medical issues - then jumped in the icy reservoir.
However, his friends could see he was panicking, and one of them - only identified as C in the case - bravely jumped in after Sam in a bid to rescue him.
Eyewitness in the case told the investigators that he could hear Sam calling "help me, help me" after seeing many "young boys laughing and joking around".
"I could see four teenage boys, it sounded like they were getting more excitable," he said.
"It appeared like they were egging one other to jump into the water.
"One of the teenagers then started shouting: 'Help me, help me'. I went to see what was happening not realising the urgency until I got next to the side of the bridge. It all happened so quickly.
"We assisted the teenager hanging onto the bridge, ('C'), and between us we managed to get him out of the water.
"He kept saying: 'Where's my mate, where's my mate?'"
the inquest came to know how a throw line was unsuccessfully used to try to pull Sam from the water before firefighters came to the scene - with one jumping into the reservior to help Sam.
However, unfortunatelly Sam had drowned , and his dead body was recovered.
Investigator identified as Nichola Mundy concluded Sam passed away from drowning, and that his death was an accident as she lauded his friend's attempts to rescue him.
"Because he didn't have any fear or sense of danger he said he would jump in first," she said.
"The temperature of the water would have been a significant shock to Sam and to Sam's system that would have sent him into panic. His friend's efforts to save him were valiant.
"His friend was very brave but it simply was not possible him to save his friend despite his best efforts."
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