Lewis Eddleston of Doncaster disappeared Sunday. His body was discovered Wednesday morning about a mile from the place he was last seen.
The post-mortem examination determined Lewis drowned. Police said the death is not believed to be the result of foul play.
Lewis's family told the BBC they felt police did not take the boy's disappearance seriously after he was reported missing. But police said the investigation was complicated by false reports on social media sites that he had been seen alive.