Teenagers Tomi Solomon and Samuel Haycock both died following separate incidents in the River Calder and a reservoir near Rotherham in the last week.
Tomi, 13, a talented young footballer who played for the academy at Bradford City, was seen getting into difficulty in the river in Brighouse while playing with friends on Tuesday afternoon, West Yorkshire Police said.
Police in South Yorkshire named 16-year-old Samuel as the teenager who died in an incident at Ulley Reservoir on Friday afternoon last week.
A GoFundme page set up by a friend has already raised more than £2,700 for Sam's family following the tragedy, in which it has been reported the teenager had jumped in to rescue a friend who had gotten into trouble in the water.
Outside Yorkshire, several other incidents have occurred in rivers and reservoirs resulting in tragedy, including a man who died after being pulled from the River Thames in Buckinghamshire on Monday and a man who died after entering the River Ythan in the Scottish Highlands on Thursday last week.
Yorkshire Water, which owns most of the region's reservoirs, and the Canal & River Trust are among the raft of authorities pleading with the public to be aware of the dangers of swimming in open water.
Even the strongest of swimmers are defenceless if they are caught in strong currents, experience the shock of freezing water or get stuck in debris, experts say.
Meanwhile the risk of incidents increases over the summer and during spells of warm weather.
Andy Rose, group manager at West Yorkshire Fire and Rescue Service, said: “Unfortunately, during periods of warm weather we tend to see these figures rise with people entering canals and rivers to cool down and swim.
“As appealing as this may seem, there are many hidden dangers that have tragically taken lives and I would urge members of the public to think twice before entering due to the potential unseen hazards and risks."
The waterway and wellbeing charity Canal & River Trust looks after a total of 2,000 miles of canals and rivers across England and Wales, as well as 72 reservoirs.
Sean McGinley, director for the charity's Yorkshire & North East branch, said: “There may be hidden dangers such as unexpected currents and submerged objects which can quickly cause even the strongest swimmer to get in trouble or cause injury.”
Gaynor Craigie, head of land and property at Yorkshire Water, said: “As the weather warms up it is important visitors to our reservoirs are not tempted to get into the water to cool off. Sadly, we’ve seen recently the dangers water can pose and it is important visitors to our sites understand entering a reservoir can be dangerous.
“Low water temperatures can cause cold water shock that may lead to hyperventilation, increased blood pressure, breathing difficulties and ultimately death. Underwater machinery and the currents associated with their operation are also a potential hazard for people choosing to enter the water.
“We recently backed the National Fire Chiefs Council’s Be Water Aware campaign and would encourage those visiting our reservoirs to do so safely, which means not entering the water and putting themselves at risk.”
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