Sheriff's deputies said Seth Welty, 16, of Canton and his passenger struck a watercraft operated by Derek Vermeulen, 20, of Tipton, who was drifting on the west side of the lake Wednesday afternoon.
The impact sent the three into the water. Mr. Vermeulen was not injured, deputies said.
Seth and his passenger were taken to a local hospital before being transferred to C.S. Mott Children's Hospital in Ann Arbor, where both were listed in good condition yesterday.
Deputies said Seth suffered a broken arm and a possible broken back.
His passenger, who deputies identified as Allison Vermeulen, 15, sustained a possible broken neck, although the hospital would not confirm their injuries. The hospital identified the girl as Alissa Vermeulen.
Lenawee County sheriff's Lt. Cletus Smith said citations were pending and would include careless operation and boater-safety violations.
Michigan requires operators of personal watercraft to take a boaters' safety class.