Children and adults are being warned of the dangers of swimming or diving in rivers.

With the school holidays in full swing, the Environment Agency and Thames Valley Police are reminding people of the hidden risks of the county's rivers, lakes and ponds.

People are advised not to jump off bridges in a bid to cool down, and also reminded not to vandalise lifebelts along river and canal banks, which has been an on-going problem in Oxford.

There are several fatalities each year, and it is estimated that on a warm summer day, between 50 and 100 children will be found playing unsupervised along popular spots along the River Thames.

In 2002, 12-year-old Nathan Monaghan, of MacKenzie Avenue, Milton Heights, near Didcot, drowned after falling into the Thames while fishing with a friend near weirs at Sutton Courtenay.

And last October, William Lovelock, 27, an engineer based at RAF Benson, jumped from Shillingford Bridge into the River Thames, hit his head and drowned.

Pc Paul Phillips, of Thames Valley Police, said: "In Oxford last year there were a number of reported incidents of people jumping from river bridges -- this is extremely dangerous and can result in serious injury or even fatality due to possible hidden dangers, such as bicycles, shopping trolleys and glass bottles in the water. We have also experienced problems with people tampering with life-saving equipment -- this is a very serious offence as someone's lives may depend on it. Offenders will now be dealt with by the courts."

Children are also being warned to be aware of overhead power lines when playing this summer. They are reminded not to fly kites or model planes near cables, and to make sure they are well away from any overhead lines when fishing.