Police are trying to find out what caused a Waterloo woman to drive into a lake this morning. The woman was dead by the time rescuers reached her. Evansdale Police Chief Michael Burke says they’re trying to determine why the van driven by 53-year-old Janice Alderman of Waterloo left I-380 and plunged into Eagle Lake around six A.M. He says they’re looking into a preexisting medical condition. Burke says Alderman was trapped in 15 feet of water for about 45 minutes before rescuers could get to her. She was dead when pulled from the vehicle.