What is cold water shock? Why is it dangerous?

PORTLAND, Ore. (KOIN) -- The early summer heat wave in 2024 in Oregon is one reason many people will go to lakes and rivers to cool off. But even though the temps are hot, the water is not -- and that sets up cold water shock.

"We're expecting the Sandy River, where Oxbow Regional Park is, to be in the low-60s," said Hannah Erickson, a communications specialist with Metro Parks and Nature. "Now, when you have a temperature change that is that big between air and water, that is a set up for what's called cold water shock, and that can make your body clench up so much that it's not able to swim."

It's always important to wear a US Coast Guard-approved life jacket, which needs to be the correct size. Erickson said there is literally a good rule of thumb for finding if a life jacket is fitting correctly.

When you put one on, make sure all the straps are tight. Then, she said, "You put your thumbs underneath the lifejacket, and if you can pull it up past your ears then it is not tight enough."

Metro Parks and Nature offers life jackets that people can borrow for free at their parks and boat ramps.

Swimmers also need to be aware of their surroundings.

"Unlike a swimming pool, there will be unexpected drop offs in a riverbed or a lakebed. There can also be underwater snags that you're not prepared for that can catch your feet, as well as currents and sudden temperature changes," she said.

About 50 people drown in Oregon waters every year, officials said. About 35 of those accidental drownings are teenagers.

KOIN 6 News will have more information later.