It was a record year for snow in many parts of the West -- and as summer approaches, that snowpack is melting fast. That's good news for whitewater rafters, but it can be deadly for casual swimmers.

At least five people have already drowned this year in California's Sierra Nevada, home to some of the fastest uncontrolled rivers in the West. On a recent day in Sequoia Kings Canyon National Park, about a dozen rangers dressed in thick wetsuits and brightly-colored helmets participated in rescue practice exercises.

Even these fit and highly trained rescue rangers are gulping water and gasping for air during some of the exercises. This, despite being dressed in wetsuits -- better protection than an average tourist is likely to have. The 45-degree water usually saps people's strength in less than five minutes, says ranger Ned Kelleher.

"People underestimate the strength of the water and how cold the water is," Kelleher says.

This summer, volunteers will join trained rangers to patrol the riverbanks in this park. They will warn visitors to stay out of rivers until later in the season, when water levels are lower come down and it is safer to swim.

Sasha Khokha is a reporter with member station KQED in San Francisco.

Copyright 2022 NPR. To see more, visit https://www.npr.org.