A missing 4-year-old boy who was swept away with his 8-year-old sister in a raging California river over the weekend was found dead Monday, a day after searchers recovered the girl’s body, authorities said.

Rescue personnel spotted the boy beneath the water against a tree in the Kings River, about 1.75 miles from where he and his sister initially entered the turbulent water on Sunday, the Fresno County Sheriff’s Office said. 

The search for the siblings began around 2 p.m. Sunday after the pair fell into the cold river and were swept downstream, officials said.

The children had entered the water with their mother and her adult friend about a mile down from Pine Flat Dam while trying to climb onto a specific rock, according to the sheriff’s office.

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turbulent King River

Searchers found the body of the 4-year-old boy caught against a tree underneath the water on Monday morning. (Fresno County Sheriff's Office)

Neither child was wearing a life jacket.

Deputies and Cal Fire firefighters responded with rescue boats and launched a search.

King River

The body of the 8-year-old girl was found Sunday, less than an hour after the current carried her away. (Fresno County Sheriff's Office)

Less than an hour later, the 8-year-old girl was found dead about .2 miles from where the current carried her away. Her brother, however, remained missing.

On Monday morning, about 40 rescue personnel continued the search for the missing boy using boats, a remote-controlled vehicle in the water, drones and a helicopter.

Pine Flat Dam

The children, their mother and her adult friend entered the turbulent King River about a mile down from Pine Flat Dam, officials said. (Fresno County Sheriff's Office)

No additional information about the children’s deaths was immediately released.

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Both the Kings and San Joaquin rivers have been closed to recreational users since March.

Authorities warned that "heavy winter storms and melting snow … have created high water levels and hazardous conditions."

"The water remains cold, in the low 50s, the current is swift and trees serve as dangerous obstacles," the sheriff’s office said.

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The rivers will remain closed until the "extraordinary dangerous conditions" improve, officials said.