On November 3, 2018, about 0940 Alaska daylight time, a Cessna 172 airplane, N2809L, sustained substantial damage during an emergency landing on runway 25 at Merrill Field (PAMR), Anchorage, Alaska. The airplane was registered to and operated by the pilot as a 14 Code of Federal Regulations Part 91 visual flight when the accident occurred. The private pilot was uninjured. Visual meteorological conditions prevailed and no flight plan had been filed for the local area flight. The flight had departed PAMR about 0935. According to the pilot, on a previous flight, about 0900 the same day, when around 400 ft above ground level (AGL) during climbout, the engine began losing power and ran extremely rough. While in the traffic pattern, the engine was only able to produce about 1200 RPM. The pilot stated that he was able to return for an uneventful landing on runway 25. Following the event, the pilot sumped both fuel tanks and gascollator for containments, with none found. The pilot then completed a run-up with no anomalies and taxied for departure with the carburetor heat on. Upon reaching the run-up area, the pilot completed another run-up. With no anomalies occurring on either run-up, the pilot elected to depart for a flight around the traffic pattern. Just after departure from runway 25, and around 300 ft above ground level (AGL), the engine again began losing power and ran extremely rough. An emergency was declared and the pilot was able to return for landing. During landing, the left wing impacted the runway, resulting in substantial damage. After the second event, the airplane was parked outside where temperatures remained below freezing. On November 4, the airplane was examined by the NTSB Investigator-in-Charge. The fuel caps were found frozen in place due to a significant amount of water trapped in the recessed area. Upon removing the caps, ice was found on the vent flap and the filler neck was completely covered in corrosion. Corrosion particles were also located within the fuel tank. The gascolator was then drained and tested for water by use of a water finding paste. The fuel sample tested positive for water. Due to the cold outside temperatures, draining of the carburetor was delayed to allow for thawing of all potential ice in the fuel system. On November 12, the carburetor was removed from the airplane by Alaskan Aircraft Engines, an overhaul facility, for inspection. According to the inspection report, a large amount of debris and water were located within the carburetor bowl.