On May 23, 2004, about 1900 eastern daylight time, a Cameron Balloons N90, N6123U, sustained minor damage while landing in Whately, Massachusetts. The certificated commercial pilot and three passengers were not injured, while one passenger sustained a serious injury. Visual meteorological conditions prevailed for the flight that departed Conway, Massachusetts, about 1800. No flight plan was filed for the sightseeing flight conducted under 14 CFR Part 91. The pilot reported that the surface winds were very light during takeoff; however, the wind velocity increased during the flight. Due to the increased wind velocity, the pilot located an open field to land the balloon. During the approach, windshear drove the balloon into trees. The balloon then became entangled in trees about 10 feet agl. A tree limb subsequently broke, and the balloon fell to the ground. During the fall, a passenger suffered a fractured leg. The reported weather at an airport approximately 20 miles south of the accident site, at 1853, was: wind variable at 4 knots; ceiling 4,900 feet overcast; temperature 73 degrees F; dew point 66 degrees F; altimeter 29.83 inches Hg; remark lightning in the distance to the south and southwest. The reported weather at an airport approximately 20 miles northeast of the accident site, at 1852, was: wind variable at 6 knots; ceiling 11,000 feet overcast; temperature 68 degrees F; dew point 60 degrees F; altimeter 29.88 inches Hg.