On September 27, 2018, about 1500 Alaska daylight time, a float-equipped Cessna A185F airplane, N70391, sustained substantial damage during a forced landing following a total loss of engine power while in level cruise flight near Fairbanks, Alaska. The airline transport pilot was not injured. The airplane was registered to and operated by the pilot as a 14 Code of Federal Regulations Part 91 visual flight rules (VFR) flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed Chena Marina Airport (AK28), Fairbanks, Alaska for an unknown lake in the Minto Flats near Fairbanks, Alaska with a planned return to AK28. According to the pilot, prior to departure for the 24-minute round trip flight, the airplane was refueled and a total of 25 gallons of useable fuel was on board the airplane. The fuel quantity was confirmed with a custom-made fuel dipstick prior to departure. After landing at an unknown lake in the Minto Flats, the pilot departed for the return leg to AK28. While in level cruise flight, at an altitude of about 1,000 feet above ground level (AGL), the engine lost all power. In an effort to restore power, the pilot switched fuel tanks and activated the fuel boost pump. When power was not restored, he performed an emergency descent to a small lake. During the emergency descent and landing, the airplane impacted trees, the floats separated from the fuselage and the airplane came to rest partially submerged, resulting in substantial damage to the wings and fuselage. A postaccident examination of the airframe and engine revealed that both left and right fuel tanks were intact and about 35 gallons of fluid was drained from the tanks. Of that 35 gallons, about 2 gallons of fuel was recovered. Examination of the fuel bladders revealed that both left and right bladders were loose in the tank cavity with wrinkles present. The fuel line between the fuel pump and the fuel control unit was removed and about 2 tablespoons of fluid light blue in color consistent with 100LL AvGas was recovered. The fuel line between the fuel control unit and fuel manifold was removed and no fluid was present. The airplane was equipped with optional long-range fuel tanks. According to the Cessna 185 Owner's Manual, the total unusable fuel for an aircraft equipped with long range fuel tanks is 6 gallons. Examination of the Continental IO-520 engine revealed no anomalies, or evidence of malfunction in any of the accessories. The cylinders, piston, valve train and crankshaft, and other internal components were all without evidence of anomaly or malfunction.