Twelve hydropower schemes have been proposed for the Lao, Lao-Thai and Cambodian reaches of the Mekong mainstream. Implementation of any or all of the proposed mainstream projects in the Lower Mekong Basin (LMB) could have profound and wide-ranging socio-economic and environmental impacts in all four riparian countries. The main report document was prepared for the Mekong River Commission Secretariat (MRCS) by ICEM – International Centre for Environmental Management engaged to facilitate preparation of a Strategic Environment Assessment (SEA) of proposals for mainstream dams in the Lower Mekong Basin. This current report is an excerpt of the whole study, and focuses on fish resources only.