People cool off in a fountain in Lyon as a heatwave hits France, on May 27, 2026. [AFP]

The UK's Royal Life Saving Society on Wednesday issued warnings on water safety after nine people died in the sea, rivers and lakes during days of record-breaking hot weather.

Tuesday saw the records for the hottest day in May broken in England and Wales, with temperatures reaching 35.1C at Kew Gardens near London.

Seven of the nine water-related deaths reported by police in England and Wales since Sunday have involved teenagers or young children.

The RLSS warned that in the UK when air temperatures reach 25C, "there is a fivefold accidental drowning risk" and teenagers and young adults are "proportionately more likely to lose their lives".

The National Water Safety Forum said Wednesday that "periods of hot weather often correlate with a rise in accidental drownings".

In the UK, inland waterways have accounted for more than half of accidental drowning deaths since 2019, as water there often "stays dangerously cold all year round", the charity said.

On Tuesday, a 17-year-old boy drowned in a lake in Cheshire and a 12-year-old boy died after getting into difficulty in a river in Lancashire, police from the regions of northwestern England said Wednesday.

A teenager's body was found Wednesday in a lake in Hampshire, southern England, local media reported.

These deaths came after four earlier reported deaths from drowning involving teenagers in England since Sunday.

In Lincolnshire in northeast England, a 15-year-old boy drowned Sunday, police said.

The father of the boy, named as Declan Sawyer, issued a warning to other families about the dangers of children "playing near any rivers and lakes in the hot weather".

A teenage girl was pronounced dead after being pulled out of water Monday at a water park in Warwickshire in central England, police said.

In Yorkshire in the northeast, one boy drowned in a reservoir Monday and a 13-year-old boy's body was recovered early Tuesday at a country park, police said.

Two older people also died in water-related incidents during the heatwave: in Cornwall, a man in his 60s died Monday from a cardiac arrest while trying to assist family members in the sea and a 72-year-old woman was pulled from the sea in Wales on Sunday and died at the scene, according to local police.