Why Jumping Into Cold Water Can Be Risky

Lakes and rivers often stay cold during a heatwave because air warms faster than water.1 During the spring and early summer, water temperatures may remain low even after several days of hot weather.

“Let’s say I go to the lake on Memorial Day and Labor Day. Maybe the air temperature is the same, but the water temperature is much warmer at Labor Day because it spent the last three months warming up,” Zachary Schlader, PhD, an associate professor of kinesiology at Indiana University School of Public Health – Bloomington, told Verywell.

That temperature difference can have serious consequences. Suddenly entering cold water can trigger the body’s “cold shock response,” causing an involuntary gasp, rapid breathing, or even heart problems. The water doesn’t have to feel frigid—water as warm as 77 degrees Fahrenheit can trigger this response.


A gasp can cause people to inhale water right away.

“We’ve all been there when you walk into what you expect to be a hot shower, and it’s cold—you jump in, and you gasp. That’s the first thing that tends to happen, and that reaction has been associated with drowning in extremely cold water,” Schlader said.

It is possible to drown within minutes of plunging into cold water. The danger isn’t simply being in cold water, but it’s the body’s reaction to the sudden temperature change.

While you could experience cold shock in a swimming pool, these are typically not as dangerous because most pools are kept above 77 F.

Dehydration May Increase the Risk Further

During a heatwave, it is especially important to stay hydrated. Drink plenty of water and limit alcohol and sugary or highly caffeinated drinks, which can contribute to dehydration.

When you’re dehydrated, your blood volume drops and your heart rate has to work harder to maintain blood pressure.

Since cold shock mainly affects your cardiovascular and central nervous systems, being dehydrated when you jump into the water could potentially amplify the risk, said Ryan Marino, MD, an emergency medicine physician and an associate professor of emergency medicine and psychiatry at Case Western Reserve University School of Medicine.

People with circulation or heart problems should also avoid jumping into the water for that reason.

“Younger people, presumably with stronger cardiovascular support, should be less predisposed to that, but as we can see, it’s very easy for it to happen. It can happen very suddenly, and it’s completely an involuntary response from the body,” Marino said.
How to Enjoy a Cold Swim Safely in Extreme Heat

Extreme heat is the leading weather-related cause of death in the United States, so finding ways to stay cool is essential during a heat wave. You can still cool off at a beach or a lake, but the safest way to do this is to enter the water gradually by dipping your feet or splashing the water on your neck or wrists first.

Your body has the immediate cold shock reaction when it’s dunked underwater, not when you slowly wade out into the ocean because you have time to sense the cold and control your breathing, Schlader said.

“If you’re really hot, getting in the water may be better for you, because it’s going to cool you very rapidly,” he added. “Just know this could happen, so control your breathing and try to keep your head above the water.”