It has become almost tradition for youths in town to spend warm summer days hurling themselves into the Haven.

Last week shoppers came to a standstill to watch gangs wearing just their shorts jumping off Town Bridge, St Botolph's Bridge and the top of the White Hart Hotel.

Sluice Bridge is another favourite site.

But the Environment Agency has warned anyone thinking of going for a dip that they could be in too deep.

Irven Forbes, an Environment Agency waterways manager, said: "Water claims the lives of more than 50 children a year in the UK.

"In fact, drowning is the third most common accidental death among Britain's under 16s, behind road accidents and house fires.

"However, the statistics show that there is still work to do to get the message across that the hazards are often hidden, and underestimating the dangers of water can have tragic consequences."

More than half of all drownings occur in our rivers, canals, lakes and pools every year.

Figures show 179 people drowned in inland waters in 2005.

Last week Boston police moved on the youths who were jumping off the bridges and White Hart.

"During the hot weather we inevitably get an increase in calls from members of the public concerned for youngsters hurling themselves into rivers," said Insp Phil Clark, who warned of the dangers of debris lurking below the surface, strong and tidal undercurrents and deep, suffocating mud that could trap anyone venturing in.

"We know that any water is tempting when the temperatures are soaring, but we cannot stress enough how dangerous it is to use waterways to cool off in."

White Hart manager Alan Bloomfield says his staff are taking measures to prevent jumpers throwing themselves off his business.

He said: "We'll do the same as every year – keep an eye out.

"If it's happening we'll try to stop it happening.

"We ask people not to jump off. If someone was to injure themselves or worse that comes back to me – and I don't want anything like that on my conscience."



Don't mess about on the river:

The Environment Agency's tips if someone's in danger in the water

l Get help: ring 999 or get someone else to do it. Alternatively if you are on your own without a mobile phone, call for help if you can see people are nearby, or go and get help.

l Think: of your own safety first. Don't put yourself in danger by going into the water to rescue someone – you may get in trouble in the water too.

l Reach: a stick, scarf or clothes tied together can help you reach the person. Crouch or lie down to avoid being pulled into the water yourself, or…

l Throw: a rope is best because you can then pull the person in. If you don't have any rope, throwing something in that will float, such as a ball, a plastic bottle or a lifebuoy, will assist in keeping the person afloat until help arrives.