THE PILOT REPORTED THAT HE FORGOT TO RETRACT THE WHEEL PORTION OF HIS AMPHIBIOUS FLOAT EQUIPPED AIRPLANE FOLLOWING A TAKEOFF FROM A HARD SURFACED RUNWAY. SHORTLY THEREAFTER, HE LANDED IN THE WATER WITH THE WHEELS EXTENDED AND IMMEDIATELY NOSED OVER. THE PILOT SAID THAT HE FELT RUSHED DURING HIS PRECEDING TAKEOFF DUE TO A POTENTIAL AIR TRAFFIC CONFLICT, AND HE SUSPECTS THAT HIS CONCERN FOR THE LOCATION OF THE APPROACHING TRAFFIC INTERRUPTED HIS NORMAL HABIT OF RETRACTING THE GEAR.