The girl was pulled unconscious from 12ft of water at the deep end of a public pool in Bangor, North Wales, when underwater cameras spotted that she was not moving and alerted a lifeguard. The lifeguard could not see the girl in the crowded pool but was able to respond to the alert within seconds.

It is the first time in Britain that the Poseidon surveillance system, manufactured by a French company, has helped lifeguards to save a swimmer from drowning. The campaign group Swimsafekids said last night that the rescue proved that the system could save many more lives if they were installed compulsorily.

The state-of-the-art system has been credited with saving three swimmers in France. Last year it helped to save a middle-aged German man who had a heart attack. So far, eight pools in Britain have installed the system.

The girl, from Rochdale, Greater Manchester, was on a camping holiday run by a charitable trust near Bangor. Along with her friends she was having a lunchtime swim on August 24 when she got into difficulties.

Karen Gibson, the lifeguard on duty, said: “You cannot see people at the bottom when there are people swimming because it is so deep — let alone during the summer holidays when there is so much splashing and activities.”

Brian Evans, Gwynedd Council leisure officer, said that the system identified the girl at the bottom of the deep end “quicker than the human eye”.

“The Bangor pool is typically 1960s design with lots of windows, which creates a lot of glare on the surface of the water and can make it difficult for lifeguards to see what is going on. It is also very deep at 12ft. Those two factors led to us installing the system.

“What is a cost like that when you can save a person’s life like it did here? It showed how quickly someone can be saved. We got it right in time. Any longer and her heart would have stopped.”

The Poseidon system, developed by the French Vision IQ company, was installed two years ago at a cost of £65,000.

A series of cameras in and outside the pool monitor the movements of swimmers, matching the images with a database to detect those in distress or apparently unconscious. It constantly scans the pool analysing the trajectories of swimmers. Poseidon sounds an alarm on a screen at the lifeguard station, picturing the stricken swimmer and indicating the position.

There are eight cameras in the water and another ten above the water line at Bangor. Manufacturers say the system operates as a “third eye” for the lifeguard. In this case, the girl was identified and rescued within 62 seconds.

Francois Marmion, general manager of Vision IQ, said: “It is virtually impossible for lifeguards to see everything that is happening in the pool all of the time, given the warm, noisy and crowded environment in which they typically work. This is very important for us because it is the first time the detection system has helped lifeguards to save somebody from drowning in Britain.

“It took six years to develop. It is a pretty complex piece of software behind the system. There is no equivalent system anywhere elese in the world.”

Poseidon has been fitted in more than 120 pools across the world, including the US and Japan, and will soon be introduced in Australia.

Penny Matthews, founder of Swimsafekids, has urged local authorities to buy the system.

Mrs Matthews, whose son, Nathan, drowned in the Thames Leisure Centre’s Jubilee Pool in July 2004, said: “This proves to people that the system does work. It would cost only £1.75 per child per year to install them in all public swimming pools.”

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