Cold water kills even in a heatwave: why temperature belongs in your trip plan

May 2024 was the warmest May the UK had ever recorded. It was also the deadliest month of that year on the water: 28 of the year's 193 accidental drownings happened in it. Warm air, cold water. The sea and inland water around the UK sit at about 12°C, well below the 15°C the RNLI calls cold, and that gap is what catches paddlers out.

Air temperature is the number you feel, and the one that fools you. The water underneath does not follow it. Average sea temperatures around the UK and Ireland are just 12°C, and inland water stays cold for most of the year. As the RNLI's Ross Macleod puts it, open water 'may look inviting during hot weather, but it remains cold enough year-round to trigger cold water shock.' A hot day does not warm the water. It just makes the cold water more tempting.

Anything below 15°C counts as cold water, and it does not need to be far below to be dangerous. Cold water shock hits in seconds: an involuntary gasp, breathing you cannot control, a spike in heart rate. The RNLI warns it can cause heart attacks 'even in the relatively young and healthy'. Cold water shock does not care whether you can swim, because your body stops doing what you tell it before you can swim at all. Fall off your board into 12°C water and the first minute is the one that matters.

Most people check the wind and the sky. Fewer check the water, because it does not feel like a forecast item on a warm day. The numbers say it should be. In 2024, 61% of accidental drownings in the UK happened at inland waters, and many of the people who died never meant to go in at all. On a paddle, going in is part of the deal, so cold water is not an edge case. It is the normal state of the water you are standing on.

The answer is not to stay home. It is to dress for the water rather than the air: a wetsuit or the right layers, a leash so your board stays with you, and a way to get back on quickly if you come off.

PaddleScout's Pro trip planner shows the air temperature alongside the wind at the launches you have saved, for the hour you mean to paddle. Read the air temperature as what it is: how the day will feel on the board, not how the water will feel if you fall in. No forecast turns cold water warm. When the planner shows a hot, still evening, that is the day to respect the water most, because everyone else will be treating it as safe. For the wind side of the same check, see our post on the best wind speed for paddleboarding.