Safety agencies urge the public to make water safety a priority, as throngs of residents and tourists head to rivers and lakes this Memorial Day weekend.
Local emergency responders said the leading causes of drownings are alcohol or drug use, hypothermia, lack of preparedness for strong river currents, wearing improper clothing while swimming and unexpectedly slipping into waterways while fishing or walking along riverbanks.
The most common advice for staying safe: swimming in designated areas and supervising kids, wearing life jackets and proper clothing for swimming, swimming or boating with friends, avoiding excessive alcohol consumption, and taking swim lessons.
Being cautious around water is even more important in the mountains because, at all but a few swimming holes, there are no lifeguards, and because the water tends to be cold and the rivers fast-moving and full of branches and other snags.
"Even experienced swimmers can get caught in swift river flows (or) debris or suffer from hypothermia," said Sylvia Ortega Hunter, the acting director for the California Department of Boating and Waterways.
An American Red Cross survey released early this month, in advance of summer, found nearly two-thirds of American families with children planned to swim in an area without a lifeguard this summer.
"High summer temperatures and close proximity to the many rivers, lakes and recreational areas in our region makes water safety a must," Kathleen Weis, Interim CEO for the American Red Cross Capital Region in Sacramento, said. "With the season changing, now is a great (time) to review water safety precautions so you know what to do to stay safe."
The survey also found that nearly half of Americans have had an experience where they feared they would drown.
Drownings are all too common locally.
The Tuolumne County Sheriff's Office counted six drownings in the county in 2011, three in 2012 and one so far this year, which occurred at South Lake Tulloch on May 18, according to search-and-rescue coordinator and deputy coroner Rob Lyons.
He estimated that the county averages five drownings per year, and about half involve drugs or alcohol. Statistics were not immediately available for Calaveras County.
Yosemite National Park had six water-related deaths in 2011 and four in 2012, according to park spokeswoman Kari Cobb. The park has not had any water-related deaths yet this year.
"The most we can do is educate visitors on how to stay safe around water and recognize the power of water," Cobb said.
Yosemite performed its annual water safety demonstrations Wednesday, both to educate the public on water dangers and rescue methods, and to train search and rescue personnel.
Cobb said an important thing for visitors to remember is that water is deceiving - it may look calm but can actually have strong currents below the surface.
"Water flows will fluctuate with the warming and cooling of the day so outdoor recreationists should always be prepared for a change in conditions," said Randy Livingston, vice presidentof power generation at PG&E.
"No swimming" signs are posted near Yosemite's waterfalls but park rangers expect visitors to use good judgment in other areas.
Throughout the park, rangers conduct a "Preventative Search and Rescue" program in which they discuss potential dangers with park visitors related to the trails they are on and answer questions.
At Pinecrest Lake, one of the most popular recreation areas in Tuolumne County, many injuries are caused by people jumping off rocks into the water, according to Lt. Brian Bosque of the volunteer fire department in Pinecrest.
The Red Cross survey showed that 93 percent of respondents were unsure how to help an endangered swimmer.
Weis said someone who sees a swimmer in trouble should call for help, reach out to the person or throw a flotation device, and dial 911.
"People think that if a person isn't calling out for help that they must not need help," she said. "However, they are likely using all their energy to just try to stay above water."