Despite this week's heatwave, water temperatures in Ireland are always likely to be at least 20 degrees below our body heat.
That's according to a member of Waterford Harbour Sub-Aqua Club who's urging people to exercise proper water safety.
Kevin O'Carroll says it's hugely important to know exactly what you're getting into...
"The average sea temperature around our coasts would range between 9 and 15 degrees.
"Obviously, if our body temperature is in the range of 36.5/37 degrees, when we jump into the water, that's a shift of 20 degrees which our body reacts to.
"So, this is where you would hear reports of cold water shock. Your involuntary response is to gasp. Now, if you happen to be under water at the time, obviously you're swallowing water."
It comes as Water Safety Ireland says the island of Ireland has experienced its worst week for drownings in about 8 years.
Six people have lost their lives in waterways in the Republic and Northern Ireland over the last week.
They include a man in Dublin, teenagers in counties Down and Cavan, a woman in Cavan, a man in Fermanagh, and a man in Leitrim.
Chief Executive of Water Safety Ireland, John Leech, says it's heartbreaking news:
"It's awful news. It's the worst bout of drownings we've had since 2013 when we lost 13 people in 14 days on the island. Unfortunately, we're almost coming back to that at the moment and we're very concerned at the moment because of the sheer number of people who are drowning."
Kevin O'Carroll is advising people to be aware of the dangers of cold water shock:
"The impact on your muscles and the blood vessels close to the skin's surface will immediately contract, which puts pressure on the heart.
"You just have to be careful with cold water that you acclimatise yourself.
"You'll remember as a child you run into the water and it's really cold and you run back out again. Then you run back in a second time and it's not nearly as cold.
"The water temperature hasn't changed, your body has just acclimatised that little bit. And that's the sort of stuff that we need to be aware of."
Meanwhile, Kevin is also pleading with people heading to beaches around the county to make sure they park in a responsible manner:
"When parking their cars, can they please make sure that they leave room for emergency services? That's not just the width of a car, it's the width of an ambulance.
"There was a case in Dunmore East last week where there was trouble getting the ambulance down. Thanks be to God everything worked out ok but can people please, please be careful how they park their cars?
"Emergency services need access."
