The agricultural airplane was overloaded for conditions during takeoff. The pilot reported that the airplane did not climb after takeoff and was very sluggish. He held the airplane in ground effect to gain airspeed so that he could clear the chain link fence at the end of the runway. As the pilot attempted to initiate a climb, the airplane started to descend towards a sewage pond. The pilot attempted to jettison the load, but the airplane impacted the sewage pond and flipped over. The operator estimated that the airplane's gross weight at the time of the accident was approximately 6,100 pounds. Weight and Balance Data taken from the G-164B Pilot's Operating Handbook indicates that the maximum gross weight for the G-164B with the R-1340 engine is 5,200 pounds. Civil Aeronautics Manual (CAM) 8, paragraph 8.10-4 (b) "Maximum Weight" states that establishing a maximum weight for an agricultural aircraft is not required. "In lieu thereof, maximum weights for the special purpose loads (e.g. hopper or tank capacities) should be selected by the applicant and demonstrated in a flight check."