The single-engine float plane was unable to maintain a climb after takeoff from a canal. The commercial pilot reported, that after climbing to about 200 feet, he "felt like the aircraft was slowly losing power...and was starting to descend." The only available landing area was a canal that was located 90 degrees off the left side of the airplane. The pilot elected to turn left, and estimated that while in a 30 degree angle of bank the airplane “stalled.” The pilot was able to get the wings level prior to touchdown. The airplane impacted the water in a nose down attitude and immediately nosed over and came to rest in an inverted position. The float landing gear separated from the fuselage during the impact and the airplane subsequently sank. The pilot and his passenger received minor injuries. The reason for the reported loss of power was not determined.