The pilot stated that he was departing on a post-maintenance flight check in a float-equipped airplane from a short waterlane, at a remote unimproved seaplane base. While taxiing for departure, he left the wing flaps in the up position to aid in turning the airplane on the water. After aligning the airplane for the takeoff run, he applied full power and the airplane accelerated onto the step. While attempting to rotate, he realized that he had forgot to reset the wing flaps to the takeoff position. He attempted to reset the manually operated hydraulically actuated wing flaps, but the airplane impacted the waterlane's far bank sustaining substantial damage to the left wing, and left-wing strut. The pilot stated that there were no preaccident mechanical anomalies that would have precluded normal operation. In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the pilot stated that the accident may have been prevented if he would have utilized the airplane's checklist or rechecked the position of the wing flaps.