HISTORY OF FLIGHTOn September 7, 2024, about 0924 Alaska daylight time, a Bell 206B helicopter, N306FW, sustained substantial damage when it was involved in an accident near King Salmon, Alaska. A passenger was fatally injured; the pilot and three passengers sustained minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 flight. The accident helicopter, owned and operated by Egli Air Haul, was transporting four passengers to a sport fishing camp located to the south of the King Salmon Airport (AKN). According to archived FAA data, the accident pilot contacted the AKN control tower specialist on duty to request a special visual flight rules (SVFR) clearance to depart to the south. The controller on duty issued the pilot a SVFR clearance and instructed the pilot to report clear of the Class D airspace to the south. The helicopter then departed to the south. Shortly after the helicopter departed, the control tower specialist received a phone call from an observer to the south of the airport indicating that a helicopter had just crashed into the Naknak River, near Grassy Point. The control tower specialist then attempted to reach the departing helicopter, but no further radio communications were received. The pilot reported encountering a very dense fog bank while flying over the calm water of the Naknek River; he subsequently lost all visual reference and became disoriented when he attempted to climb. The helicopter then descended and subsequently impacted the surface of the river. Witnesses reported that it was foggy at the airport before the helicopter departed. One witness, who was walking along the riverbank, reported that it was so foggy that she could not see the opposite side of the river. This witness saw the helicopter just before the impact and stated it was flying less the 100 ft above the water. WRECKAGE AND IMPACT INFORMATIONThe fuselage was intact with all major components still attached. The tail rotor blades, and gear box were undamaged. Cyclic and collective flight controls were traced from the cockpit controls to the pitch control rods attached to the main rotor hub assembly. Anti-torque control (yaw) was traced from the anti-torque pedals to the tail rotor with fractures consistent with impact damage at the bottom and top of the flight control “broom closet.” Tail rotor pitch control operated smoothly and freely. No damage was observed with the flight control hydraulic servos. All hoses were attached and undamaged. All fuel, oil, and electrical lines in the engine compartment were undamaged and connected. The fuel control unit was undamaged. Throttle control from the cockpit was traced to the fuel control unit. Rotational scoring was observed on the tail rotor drive shaft under the engine and on the input shaft to the K-flex. SURVIVAL ASPECTSThe passenger who was fatally injured was unable to exit the helicopter when the helicopter went under the water. The passenger was in the front left seat using a 4-point seatbelt restraint system.