On hot days, a dip in a reservoir may appear like a great way to cool down. The still water may seem harmless, but it's actually a dangerous killer which can claim a life in minutes!
What are the dangers?
There are three main dangers - strong currents, the cold and time
Strong currents - these lurk beneath the surface, particularly if water is being taken out through massive pipes beneath the surface.
The cold and hyperventilation - when fatalities occur, it's the temperature of the water which is often the most significant factor. Reservoirs are deep and the water in them doesn't flow like in rivers or the sea so the temperature rarely rises much above 12
Immersion is enough to take most people's breath away but what they probably don't realise is that this sensation is their body's natural defences kicking in - and they will only protect a swimmer for a matter of minutes, no matter how confident they are in the water.
One of the first signs of trouble is hyperventilation as the body tries to increase the flow of oxygen into the blood to help stave off the cold but, if the swimmer remains in the water, the body will begin to shut down to protect the vital organs. Muscles will go into cramp and suddenly it's no longer possible to swim. The victim will try to fight to stay on the surface but, if help doesn't arrive within seconds, they will be drawn unavoidably underwater, even though they may still be fully conscious and aware of what's happening.
Time - even if friends or relatives dial 999 within minutes of a swimmer disappearing, the reality is that the emergency services are more likely to be dealing with the recovery of a body rather than a rescue.
Firefighters, police and paramedics may be able to reach the scene within minutes, but if the victim is still somewhere in the water, they'll not be able to begin a search until specialist equipment arrives. Instead, they can only watch and wait, which may be hard for onlookers to understand but is often as traumatic for the emergency services as for family or friends of the missing swimmer.
It can take days to recover a body from a reservoir. In the meantime, friends and loved ones can do nothing more than return home and begin a tortuous wait for news.