Safety campigners have urged people enjoying the hot weather to cool off in the water only at supervised locations after a spate of accidents left two teenage boys dead and a third missing.
As temperatures soared past 30C (86F) in the first week of the school holidays, the Royal Society for the Prevention of Accidents (RoSPA) asked people to stay away from rivers, quarries and lakes and head to beaches, lidos and swimming pools instead.
On Tuesday, Aaron Burgess, 14, died while cooling off in a stretch of the River Avon between Bristol and Bath, while in Northamptonshire the body of a 15-year-old boy was pulled from the River Nene at Woodford near Kettering.
Jay Burgess and his partner Carrie Valentine look at floral tributes left at the scene by the River Avon where Mr Burgess's son Aaron drowned
Rescue workers are searching for a teenage boy who went missing after falling into the water at a quarry in Lower Gornal in Dudley.
David Walker, head of leisure safety at RoSPA, said: "We understand the temptation to want to go swimming in rivers, quarries and lakes, especially during the recent hot weather.
"Among the hazards to consider at inland waters are that, even on a hot day, water might be a lot colder than you were expecting and there may be strong currents and underwater debris that you cannot see from the bank.
"Consider how you are going to get out of the water before you get in, and be honest about your ability to look after yourself, and others, in and around water.
"RoSPA's advice is to go swimming at properly-supervised sites, such as beaches, lidos or swimming pools, although we appreciate that not everyone can get to these locations."
More than 50 friends of Aaron Burgess have laid flowers and cards and lit candles next to the River Avon.
The 14-year-old, from Longwell Green, near Bristol, was cooling off and sliding down a weir when he disappeared under the water around 5.40pm and did not resurface. Police divers found his body six hours later.
More than 50 friends from Aaron's school and youth club have laid flowers and cards and lit candles at the scene.
Floral tributes are left at the scene by the River Avon in Saltford after Aaron Burgess drowned
Aaron's father paid tribute to his "beautiful son" who was "always acting the fool" on a card laid next to white and purple flowers.
Jesse Stroud, 14, was playing in the water with Aaron when he started to struggle to keep his head above the water.
He said a group of about seven boys had been making the most of the first sun of the summer holidays after finishing school two weeks ago.
"We went down the weir just as a slide," he said.
"He (Aaron) wasn't a very good swimmer and he just started to struggle and me and my friend tried to help him, but we just couldn't and then we went over to the bank and tried to call for help.
"He was trying to keep his head above the water and was really struggling and my friend was shouting at me to help him, we were both just trying to keep him above the water.
"Towards the end, when people actually realised he was in trouble, a lot of people were watching.
"Another man got into an inflatable boat and tried to get to him.
"I was just panicking. I just couldn't believe it, because I just didn't think anything like this would ever happen. I was terrified. I never thought it would ever go this far."
Connor Wiltshire, 14, Aaron's best friend at school, said he tried to save him by paddling over on an inflatable.
He said: "I saw him fall under and I turned to a man and he had a lilo and we jumped in and tried to save Aaron but almost as we got to him to help it was too late.
"People around us were ignoring our cries for help, I think they thought we were playing."
Fighting back tears, Connor paid tribute to his friend and said he would be sorely missed.
Aaron had attended Cadbury Heath Youth Club, near Warmley, South Gloucestershire, which has around 100 members.
Many of them gathered at the river behind the Jolly Sailor pub in Saltford to comfort each other and talk about their friend.
Young girls wept and hugged each other while red-eyed boys shook their heads in disbelief.
Flowers and messages left at Saltford Weir included one from Aaron's father, which read: "My beautiful 1st born son, always acting the fool, chip off the old block, missing you loads, see you when I get there, Dad x"
Another said: "Aaron, A great friend to all. Always be missed and never forgotten. RIP. Brad Davies."
In Northamtonshire, the body of an as-yet unnamed teenager was found at 6.20pm on Tuesday, three hours after a 15-year old boy was reported missing.
West Midlands Police said they were called to a quarry behind the Crooked House Pub in Dudley at 1.17pm on Wednesday where a boy had fallen into the water.
"The police helicopter was immediately called upon to assist the search operation using its on-board thermal imaging equipment," a spokesman said.