A dive team found the body of 9-year-old Mikaela Lynch Wednesday in a muddy creek near her family's vacation home in Clearlake.
Lynch had been missing since Sunday when her brother briefly went inside the house, leaving her alone.
Police said she was unable to speak and had the mental capacity of a 1-year-old. She liked the water, but did not know how to swim.
Lynch's disappearance sparked a massive search effort that included hundreds of volunteers and law enforcement officials.
The Associated Press contributed to this report.