MENTOR, Minn. -- Two sheriff's deputies were hospitalized Wednesday morning after their airboat tipped over on a northern Minnesota lake and sank. The Polk County Sheriff's Office says the deputies were working to help county highway officials install buoys on the eastern shore of Maple Lake near Mentor, which is roughly 60 miles west of Bemidji. During the installation process, the airboat flipped over and sank to the bottom of the lake. Two highway department personnel were also on the boat when it overturned. The two deputies were brought to Essentia Hospital in Fosston with injuries that were described as "non-life-threatening," the sheriff's office said. The highway officials weren't hurt. All four were wearing life jackets. A dive team was called to help pull the boat out of the lake. An airboat is a flat-bottomed watercraft with a large aircraft-like propeller on the backend.The incident remains under investigation.