Search crews are entering their fifth day on the water in a national park in Louisiana in hopes of finding the body of a 4-year-old boy who went missing.

Ellis Boudean disappeared in the water at Jean Lafitte National Historical Park and Preserve Thursday evening, WVUE-TV reported.

Ellis, who has autism, was last seen with a parent as they visited the area that’s mostly dense swamp land, the Jefferson Parish Sheriff’s Office said.

Authorities are fairly confident that his body is in the water, a sheriff’s spokesperson said.

“At this point in time, it’s a recovery mission,” Jefferson Parish Sheriff Joe Lopinto told reporters over the weekend. “The child never resurfaced.”

The area is covered in dense vegetation and teeming with potentially dangerous wildlife, including snakes and alligators, sheriff’s officials said.

Multiple boats, sonar equipment and divers are being used in the search, Lopinto told WDSU-TV.