James Douglas (16) of Percy Street, Old Goole, owes his life to family friend Christopher Shepherdson who dived in and saved him when he started to go under.
James's aunty Kay Sumner explained: "We were just near the Waterways Museum. James had been told not to go in the water because he is not a good swimmer but he went in anyway.
"He managed to swim across okay and was told to get out and go round over the bridge but he decided to go back in and swim back across.
"He got over half way and said he couldn't do anymore and started bobbing up and down. Chris stripped off and got in.
"If Chris hadn't been there I don't know what would have happened, he would have drowned for sure.
"James owes his life to Chris."
Kay added: "I have seen loads of kids jumping in off the bridges, they need to be warned, they don't realise how strong the current is."
Chris (19), whose parents live on Mendip Avenue, was home on leave from the RAF when the incident happened.
He told the Courier: "I went to the marina near Old Goole with my girlfriend because her family were down there.
"There was a couple of lads swimming in the canal. The youngest one got to the middle and started screaming and said he just couldn't make it.
"The other lad went back to try and help but he started getting into difficulty so swam back, James started going under the water and I had to dive in to try and drag him back and save him.
"It was quite cold and I was worried because I could feel what felt like reeds under my feet.
"Everyone was crying for help so I did it instinctively."
The Royal Society for the Prevention of Accidents (RoSPA) issued a warning for people to think carefully before cooling off in rivers and lakes during hot weather.
Peter Cornall, RoSPA's head of leisure safety, said: "This is the first spell of really warm weather that we have had this year and people are rightly wanting to make the most of it by getting out and about.
"Experience from previous years has shown that we sadly see an increase in accidental drownings at times like this, and we have already heard of the drowning of a 12-year-old boy this week.
"Particularly if you are taking children to an unsupervised location to swim, you should have the skills to assess the many water hazards and know what to do if anyone gets into difficulty."