Authorities in Kern County are searching for a man in what some have called the deadliest river in America.

On Saturday, the Kern County Sheriff’s Office responded to a call for a person who was swept into the Kern River near Lake Isabella in the Sequoia National Forest. The department called upon Kern Valley Search and Rescue for help. Barbara Vargas identified the missing man as her son, Corey Vargas, on Facebook.

“Please pray for my Corey Vargas,” Barbara Vargas wrote. “… Search and rescue has not been able to find him. It’s been almost 24 hrs!!”

Corey Vargas went fishing with his son and dog when the dog fell into the water, according to a GoFundMe raising money for the family. When Vargas tried to save their dog, he slipped and fell in.

“This has been an incredibly stressful and uncertain time,” the GoFundMe says.

The Kern County Sheriff’s Office deployed multiple boat teams, drones and helicopters to work alongside deputies in the search. As of 11:30 a.m. on Monday, the man has not been found.

“The message always every year is to stay out of the river,” said Sgt. Rodney Jones with the Kern County Sheriff’s Office. “But we do know that people are going to get in the river.”

Before Memorial Day weekend, the U.S. Forest Service warned visitors to wear a “properly fitted life jacket” regardless of the activity they are doing near or in the river.