The man and several other sailors got into trouble on the river near Laton in Fresno County.
While much of the Kings River is closed for recreational use, the sheriff's office says this section near Laton is open.
They also say the group of sailors had no experience on it and they were caught off guard by an overflow dam.
The sound is almost as powerful as the water rushing through it. This is the overflow dam, also known as a weir. That caught a group of Lemoore sailors by surprise Friday afternoon.
The Fresno County Sheriff's Office searched the water all evening, looking for a man who went over the small dam and never came back up. He was part of a group, three women and six men, who just wanted to enjoy a hot day on the river.
Chris Curtice said, "They saw the weir and realized it was too dangerous to go through so they all jumped off of their raft and attempted to swim to the side."
Each sailor clutched onto brush along the south side river bank. The sheriff's office says that's when a neighbor hopped on his jet ski and tried to pull the group to the other side using a rope.
Chris Curtice said, "When they were about half way across the weight from the water and the people snapped the piece of off the Jet Ski and all 9 people started to try to swim to the side again."
At that point the sheriff's office says all 9 of the sailors were swept down the river and sucked under this turbulent water.
Several of the missing man's friends were seen walking away from the river with scratches all over their exposed skin. Four others were taken to the hospital.
Chris Curtice said, "Two of the females with minor injuries and one of the females had to be taken out on a backboard. I don't know the extent of her injuries. And one of the males had a laceration to his head."
Bradley Duinkerken lives along the river and says he's on this water a lot. "We float all the time but not this high of water."
After hours of searching the sheriff's office says their task now is to recover the missing man's body.
What's not yet clear is whether anyone in that group was wearing a life jacket.
The sheriff's office says the search for the missing sailor will continue first thing in the morning.