A coroner has warned of the "inherent dangers" of the supposed "harmless pastime" of magnet fishing after a father and son drowned while treasure hunting.

Martin Andrews, 43, and son Jack, 19, shared a passion for the hobby which involves trawling for metal at the bottom of canal and river beds by dropping a rope with a powerful magnet attached.

On Thursday, Bradford Coroner's Court heard the pair had followed the pursuit for about a year after seeing its rise in popularity in the United States online.

Angela Andrews, the wife and mother of the victims, told the hearing the whole family enjoyed the hobby "in the hope of finding a rare and valuable item one day".

They had previously pulled out shopping trolleys and "lots of car keys", but neither man had ever gone in the water while hunting for treasure, she said.

Father and son, who worked as a driver and loader at delivery firm UPS, set off from their home in Pudsey, on the early morning of June 16 this year and headed for the stretch of canal close to the River Calder in the Cooper Bridge area of Huddersfield.

Later that day, a passing dog walker rang police after she discovered items of clothing and personal possessions strewn on the canalside.

An underwater search team was deployed and the bodies of both men were discovered vertically submerged close to each other in the centre of a floodgate at about 7.15pm near to a high-sided canal bank.

Post-mortem examinations showed both had drowned and later toxicology tests confirmed both had recently used cannabis.

The court heard that Jack Andrews smoked the drug regularly, while Martin Andews was a "social cannabis smoker".

Mrs Andrews said she knew her husband had used cannabis the previous weekend, while she could "safely say" her son had not smoked it on the morning of his death.

Recording conclusions of misadventure, Senior Coroner Martin Fleming said taking cannabis may have had an impact on the pair's balance, co-ordination and reaction times, but said it could not be determined when exactly they had last used the drug.

Referring to magnet fishing, he said: "What is considered to be a harmless pastime does have inherent dangers. You throw these magnets in and it is impossible to know what is at the bottom of these waters.

"They may well have got into some trouble while engaged with this rope and equipment. We can only speculate as to how they came to be in the water.

"Plainly the fact the two of them were there may have been indicative one was trying to help the other because they were devoted to each other. The frustration is that we don't have an eyewitness."

Stephen Williamson, health and safety adviser for the Canal & River Trust, told the hearing that magnet fishing was prohibited.

He said: "It is something we try and advise people not to do because there are hidden dangers as you don't know what is at the bottom of canals."