The pilot reported that he performed a preflight inspection of the float-equipped airplane. After engine start, warm up, and taxi, he began his takeoff roll from the lake. The pilot said the airplane took longer than normal to take off and once he was airborne his airspeed was only about 40-45 miles per hour. When he lowered the nose of the airplane to gain airspeed, the “right wing started to wave up and down,” consistent with a stall. The pilot attempted to land straight ahead on the lake, but upon touchdown, the right wing impacted the water, spinning the airplane, and collapsing the right float. During the impact sequence the outboard portion of the left wing was impact-separated, resulting in substantial damage. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. Therefore, it is most likely that the pilot did not obtain the proper airspeed or angle of attack on takeoff, which resulted in an aerodynamic stall and subsequent loss of control.