The Environment Impact Assessment (EIA) undertaken for the Expansion Project identified potential physical and biological impacts on the environment as a result of the project and set out detailed mitigation, management and monitoring measures to address these during both construction and operation. THPC developed an Environmental Monitoring and Management Plan (EMMP) and established an Environmental Unit (EU) for effective implementation of these measures in cooperation with government organizations and agencies.

During project construction the EU monitored contractors' performance to ensure compliance with environmental requirements and protection standards. Following completion of the extension project, the Unit continues to monitor all environmental aspects of THPC operations including water quality upstream and downstream of the powerhouses, fish populations, and riverbank erosion.

THPC also works with partner organisations and government agencies to protect wildlife and water catchments around the project area by patrolling protected areas, encouraging tree plantations and educating local people on the importance of conservation.