During takeoff from an off airport river bank on a flight to spot moose, the airplane's left wingtip contacted tall brush. The airplane spun around, and the right wing and right main landing gear attachment sustained substantial damage. The private pilot said the winds were light and variable. He indicated to the NTSB investigator-in-charge that he had landed and taken off from the same site on previous occasions, but failed to avoid contacting the brush during this takeoff.