SANGER, Calif.—A search crew found the body of a 4-year-old boy in a surging California river May 22, a day after his 8-year-old sister died when the siblings were swept away by the current, authorities, said.

Searchers in a boat spotted the boy’s body caught against a tree in the Kings River about 1.75 miles downstream from where he and his sister went into the water, the Fresno County Sheriff’s Office said in a statement. The river has been closed to recreational use because of high water levels.

Sheriff’s deputies responded at around 2 p.m. Sunday and the girl was found dead less than an hour later. About 40 rescue personnel using boats, a helicopter, and a drone continued the search for her brother about a mile from Pine Flat Dam near Sanger, a city of about 26,000 people east of Fresno.

Officials did not immediately release the children’s names or say what killed them.

The children, who were not wearing life jackets, entered the water with their mother and another adult while trying to make their way to climb on a rock, the sheriff’s office said in a statement.

Signs have been posted along the Kings and San Joaquin rivers since March 14 urging people to stay out of the water because of hazardous conditions, the sheriff’s office said. Warming weather is melting huge amounts of mountain snow that accumulated over the winter.

“The conditions of our waterways will only become more dangerous heading into summer as snow melts and dams release even more water into the rivers,” the sheriff’s office said, noting that the water remains cold and currents remain swift.

Farther north, authorities were investigating after a body was found Friday in Folsom Lake northeast of Sacramento. And two people remained missing after being swept away by the American River in recent weeks, the Placer County Sheriff’s Office said.

Authorities have warned people to take caution along rivers throughout the state that are experiencing high water levels and stronger flows.