Heatwave drownings: Why hot weather and open water can be a deadly combination

When temperatures soar, the instinct to cool down in the nearest body of water is strong, and understandable. But water safety experts have been warning that heatwaves and open water are a dangerous combination, and the death toll across Europe this summer is making their case for them.

Europe's 2026 heatwave season began as early as May, with the first major event hitting the UK, Portugal, France and Ireland. By mid-August, the continent was enduring its fifth heatwave of the summer, with Spain recording a peak of 45.1°C.

France has recorded more than 300 drownings since mid-June, a 14% rise on the same period last year. The country's sports minister described the surge as "in line with the repeated heatwaves" sweeping the continent, noting that many deaths occurred in unsupervised or unauthorised swimming spots. 

In the UK, data shows there are around five times as many accidental drowning deaths per day when average temperatures exceed 17°C compared to cooler days.

Germany recorded its worst monthly drowning toll in more than two decades in June, with 99 people killed, the highest figure since the devastating European heatwave of 2003, when 107 people died in a single month. The German lifeguarding federation confirmed the deaths came as temperatures climbed as high as 41.7°C in some parts of the country.

The victims were predominantly young men. Of those whose ages were known, 40 were under 30, and more than 90% were male. This pattern is consistent with drowning data across Europe, where men account for the overwhelming majority of accidental drowning deaths.

Why heatwaves increase the risk

The core problem is a mismatch between how warm the air feels and how cold the water actually is. During the UK's May Bank Holiday heatwave, at least 15 people drowned in open water incidents. Many entered water that looked inviting on a hot day without realizing how cold it was beneath the surface.

Experts from the UK-based charity Royal National Lifeboat Institution (RNLI) warn that in countries unaccustomed to prolonged hot weather, the sudden arrival of high temperatures creates a particularly dangerous moment, when the urge to get into any available body of water overrides caution about what lies beneath it.

The Royal Life Saving Society explains what happens to the body the moment it hits cold water. Even on a hot day, UK and Irish sea temperatures sit around 12°C, and rivers can be colder still. Entering suddenly — by running, jumping or diving — triggers an involuntary gasp reflex. That sharp intake of breath becomes catastrophic if the person's head is underwater. What follows is a rapid rise in heart rate and breathing that can trigger panic, making it harder to stay afloat and increasing the risk of inhaling water.

This is known as cold water shock, and it was a factor in two in five outdoor drowning incidents in the UK in 2022. It can cause a rapid rise in blood pressure capable of triggering cardiac events even in young, otherwise healthy people, and a sudden loss of muscular control that makes swimming impossible. 

Experts stress that entering cold water slowly is the single most important step anyone can take to reduce this risk.

Inland water is where most drownings happen

Despite public perception that the sea is the most dangerous environment, the majority of accidental drownings occur in rivers, lakes, reservoirs and canals. In the UK in 2022, 60 percent of accidental drownings happened at inland locations.

The Royal Society for the Prevention of Accidents warns that these environments carry hidden dangers that coastal water typically does not. Former industrial sites such as quarry lakes and reservoirs may contain submerged machinery, debris and other hazards that are impossible to see from the surface. Inland locations also tend to be more remote, meaning help takes longer to arrive when something goes wrong.

The RNLI notes that people who did not grow up near water are often less aware of these risks, making water safety education in schools and communities all the more important.

The danger of trying to help

One of the most overlooked risks is the instinct to rescue. When someone gets into difficulty, bystanders often enter the water to help, but they can become casualties themselves.

The Royal Society for the Prevention of Accidents urges people to resist that instinct entirely. Entering the water to save someone else means taking on unknown hazards without knowing why the person got into trouble in the first place. This frequently results in multiple people needing rescue rather than one.

York Rescue Boat volunteers advise what is known as "reach and throw" — using a branch, a rope, tied clothing or dedicated waterside rescue equipment to help someone from the bank, while staying calm and encouraging the person in the water to float and control their breathing while help arrives.

If you end up in the water

Experts agree that the instinct to thrash and panic must be overridden. 

The RNLI advises what it calls "Float to Live:" tilt onto your back, spread your arms and legs, and let the initial shock pass. Cold water shock typically eases within a minute, and floating conserves energy while you regain control of your breathing.

Once breathing has stabilized, the Royal Society for the Prevention of Accidents advises moving arms and legs gently to stay afloat before shouting for help or swimming slowly to safety. Slowing the breathing rate helps bring the heart rate down and gives the body time to adjust, making it possible to think clearly and act.

A question of climate justice

The rising drowning toll is not only a water safety problem. Research published in a peer-reviewed journal found that the risk of unintentional drowning in the UK increases by 7% for every 1°C rise in daily maximum temperatures. So, as climate change makes hot days more frequent, drowning deaths are likely to rise with them.

But the risk is not evenly distributed. 

Children from the most deprived areas in England are more than twice as likely to drown as those from more affluent backgrounds, according to the National Child Mortality Database. 

Access to supervised pools, shaded parks, leisure centers and affordable transport to safe swimming locations varies enormously depending on where a family lives and what they can afford.

For a teenager in a hot, crowded home with no garden and no money for a swimming session, a nearby river or reservoir may feel like the only available option. Simply warning people to stay away from open water does not address the conditions that put some young people in danger in the first place.

As researchers at Loughborough University's water safety team have noted, the conversation cannot stop at individual behavior. 

If the UK is serious about preparing for hotter summers, it must build climate-safe public spaces such as supervised swimming areas, shaded parks, and affordable leisure facilities. Everyone must have access to a safe place to be when temperatures rise.