NORTH WATERBORO (AP) — Game wardens on Monday began lowering the level of a lake and forest rangers used a helicopter as the search intensified for a 15-year-old boy missing for five days.

Jaden Dremsa was last seen Thursday afternoon when he walked away from his home, and the search has been growing every day since.

Lake Arrowhead was being lowered Monday as searchers attempted to rule out areas near his home where he could be, Warden Lt. Kevin Adam said. “Anytime we ever search near water, we have to look at it,” he said.

An air-and-ground search also was continuing.

Officials say the student at Massabesic High School in Waterboro has a mild form of Asperger’s syndrome, which is sometimes described as a high-functioning form of autism.

The condition could cause the teen to try to avoid people, including those who’re trying to find him. He is described as 5 feet 9 inches tall and 140 pounds with shoulder-length brown hair and blue eyes.