On May 30, 2001, about 1155 Alaska daylight time, a float-equipped de Havilland DHC-2 airplane, N150PL, sustained substantial damage during a landing on Alexander Creek, about 1.5 miles north-northeast of Alexander, Alaska. The airplane was being operated as a visual flight rules (VFR) local area instructional flight when the accident occurred. The airplane was owned and operated by the private certificated pilot/dual student. The commercial certificated pilot/flight instructor, and the student, were not injured. Visual meteorological conditions prevailed. The flight originated at the Lake Hood Seaplane Base, Anchorage, Alaska, about 1115. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on May 31, 2001, the owner/student pilot reported the flight was the second day of instruction, conducted to gain additional experience operating on lakes and rivers in Alaska. After departure from Lake Hood, the student did some aerial maneuvering, and then proceeded to land on Alexander Creek. After touchdown on the creek in a northbound direction, the airplane was decelerating with the water rudders in the up position. The airplane suddenly veered to the right, and the floats collided with the creek bank. The left wing of the airplane collided with trees along the bank, and the propeller struck the bank. The student reported he thought the right float struck an unseen sand bar. In a telephone conversation with the flight instructor on May 31st, he reported that he was providing dual instruction to the already certificated student pilot. The instructor said the touchdown on the creek was normal until the airplane veered to the right. He said he did not know the reason why the airplane veered to the right.