On April 26, 1999, at 0900 Pacific daylight time, a Bell 212, N98W, registered to and operated by Weyerhaeuser Company, as a 14 CFR Part 133 external load operation, was substantially damaged when the main rotor blades collided with trees during a hover near Snoqualmie, Washington. Visual meteorological conditions prevailed at the time and a company visual flight rules flight plan was in effect. The commercial pilot, the sole occupant, was not injured. The flight had been performing external load operations in the local area throughout the morning. In a written statement, the pilot reported that he was moving sand, via an external load bucket, to a golf course sand trap. The pilot stated that the sand trap was located near a tree line with little room for movement to place the bucket. The trees were about 50 to 60 feet in height. The pilot reported that at the time of the accident, the bucket was placed just short of the target area. As the pilot moved the cyclic to reposition the load, the tip plane of the main rotor blades dipped down and came in contact with a tree branch. The pilot stated that he did not realize that the collision had occurred until about 15 minutes later, when he noticed the broken tree branch. The pilot landed the helicopter without incident to inspect for damage. During the inspection, substantial damage was found to the main rotor blades.