PILOT OF AMPHIBIAN FLOAT DHC2 BEAVER DEPARTED AIRPORT ON WHEELS ON VFR FLIGHT TO VILLAGE SERVED BY SEADROME ONLY. PILOT COULD NOT RECALL RAISING WHEELS AFTER DEPARTURE. PILOT MADE NORMAL APPROACH TO WATER LANDING AT VILLAGE AND UPON TOUCHDOWN, AIRPLANE NOSED OVER INVERTED. PILOT RECALLED SEEING WHEELS EXTENDED FROM FLOATS AFTER SWIMMING FROM COCKPIT.