On July 8, 2019, about 1730 central daylight time, a Robinson R22 II Beta helicopter, N334DC, was substantially damaged when it was involved in an accident near Water Valley, Texas. The commercial pilot and passenger were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight . The pilot and passenger were conducting a wildlife survey. About 1.5 hours into the flight, at an altitude between 50 and 100 ft above the top of the canyon and an airspeed of about 35 mph, the "engine began to bog" and the both the engine and main rotor lost rpm.The pilot stated that he lowered the collective, rolled the engine throttle control to full rpm, and attempted to regain the engine and main rotor rpm. The rpm continued to decay so the pilot elected to conduct a forced landing to an opening in the vegetation below the helicopter. During the descent into the vegetation the main rotor blades struck the trees. The helicopter rolled over on its left side during the ground impact. The tail boom separated from the fuselage and the main rotor blades and fuselage were substantially damaged. An examination of the helicopter and engine revealed no mechanical anomalies that would have precluded normal operations prior to the accident. The tail rotor blade fracture signatures were consistent with separation of the blades under power.