A Cessna 208B Grand Caravan sustained substantial damage in an accident near Utsingi Point on Great Slave Lake, Northwest Territories, Canada. The pilot and one passenger were fatally injured and the other two passengers were seriously injured. Air Tindi Flight 200 departed Yellowknife (YZF) at 11:03 on a VFR flight to Lutsel K’e (YSG) where it was scheduled to arrive at 11:45. Low clouds persisted for the entire flight. The pilot was flying at low level so he could maintain visual contact with the ground. Altitude during the flight varied between 129 feet and 600 feet above ground level (agl). The aircraft struck rising terrain under the pilot’s control at cruise speed, with a wings-level attitude. FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS: 1. The aircraft was flown at low altitude into an area of low forward visibility during a day VFR flight, which prevented the pilot from seeing and avoiding terrain. 2. The concentrations of cannabinoids were sufficient to have caused impairment in pilot performance and decision-making on the accident flight.