At about 1005 Alaska time, the float-equipped airplane sustained substantial damage when it collided with tree-covered terrain after takeoff. No one among the commercial pilot and four passengers aboard was injured. Visual conditions prevailed. The pilot subsequently reported he assessed the wind and water conditions indicated a downstream takeoff with a quartering left crosswind. As the airplane climbed to about 20 feet above the water, the wind subsided, and the airplane stopped climbing. The airplane then began to gradually descend and settle into the trees. According to the pilot, the airplane collided with a stand of trees, and came to rest about 400 feet from the bank of the river.