On February 13, 1999, at 1222 hours Pacific standard time, a Maule M-7-235, N747CL, was substantially damaged when the aircraft, equipped with amphibious floats, landed with the wheels extended and nosed over on Lake Mead near Boulder City, Nevada. The commercial pilot sustained minor injuries and the sole passenger was not injured. Visual meteorological conditions prevailed for the personal flight, which was operated by the owner under 14 CFR Part 91. The aircraft departed North Las Vegas at 1145 and no flight plan was filed. The pilot told the Safety Board that he had recently received training in a land based retractable gear aircraft, which reinforced habits opposite those needed for the floatplane landing on water. He failed to retract the wheels of the floatplane after takeoff from North Las Vegas because of distractions caused by radio problems and complex air traffic control procedures. He said he verified the wheel position before landing in the water but the amber wheels down indicator "didn't register."