Diving into rivers is tempting but potentially dangerous

The call comes as heatwave temperatures spread across the UK, bringing rail disruption, fear of over-exposure to the sun and a boon to the domestic holiday market.

Temperatures in Scotland are due to hit 30C in some areas, although other parts are seeing their first rain in days.

British Waterways has warned that canals, rivers or reservoirs may look inviting but everyone should resist the temptation for a dip.

"The water is frequently far cooler than expected and can bring on cramps in even the strongest of swimmers, which can lead to death by drowning," a spokesman said.

Strong sunshine

The organisation, which runs the country's canals, also highlighted the danger of underwater objects and currents created by water movement or passing boats.

Meanwhile, there have been renewed warnings to the public over the ravages of strong sunshine and high temperatures.

A warning has been issued over high temperatures

Holidaymakers, hillwalkers and outdoor workers have been advised to drink plenty of water and remember their suntan lotion.

PA WeatherCentre forecaster Lucy Verasamy said: "The best of the weather will be in the next couple of days until Sunday, when there's a chance of showers and longer periods of rain.

"Even in cooler areas there won't be much of a sea breeze and it will still be dry and sunny."

Scottish fire chiefs have asked householders and campers not to burn anything outdoors in the tinderbox conditions.

Highlands and Islands Brigade divisional officer John Donaldson said: "The effect on our resources would be massive if the fires they've had on the continent started here.

'Fire risk'

"We would find it very, very hard to cope, especially with the higher temperatures."

Hugh Adie, community safety officer with Strathclyde Fire Brigade, said: "If this weather continues there's most definitely a severe risk of such fires in Scotland."

In the countryside soaring temperatures have been creating problems for animals.

Several lambs have died from dehydration in Caithness, and vets are urging anyone with animals to ensure they have access to water and shade at all times.

Scottish Water said there were currently no plans to ration supplies, but encouraged customers to take sensible water saving measures.