The ATSB found that the pilot continued to fly after last light without the appropriate training and qualifications, and then into dark night conditions that provided no visual cues. That significantly reduced the pilot's ability to maintain control of the helicopter, which was not equipped for night flight.
Once visual references were lost, the pilot likely became spatially disorientated and lost control of the helicopter, resulting in a collision with water.
Further, the pilot did not disclose on-going medical treatment for significant health issues to the Civil Aviation Safety Authority. That prevented specialist consideration and management of the on‑going flight safety risk the medical conditions and prescribed medications posed.