Don Sahong Dam Threatens Mekong Fisheries

Map of Don Sahong Dam site
International Rivers

It is early morning along the Mekong River in Siphandone, site of the remarkable Khone falls in Southern Laos. Boats are beginning to pull up to the banks of the river, and fishers are unloading their daily catch to be sold at the nearby market. In just one season, particularly when there are heavy rains, a family in the area can earn up to 200,000 THB (roughly US$6,000) from selling fish. This same catch will also be a staple in a family’s diet. Studies have shown that wild fish make up roughly 80% of the animal protein that locals consume in this area.

Lives and livelihoods in Siphandone are intricately entwined with the Mekong River, which provides a means of transport, an economy, and most importantly, food security.

Siphandone, whose name means “4,000 islands,” is a unique and picturesque section of the Mekong River. Made up of a series of complex channels winding around small islands and inlets, it is home to extensive wetlands, and is renowned for its abundant aquatic biodiversity and rich fisheries. According to Dr. Ian Baird, a geography professor who specializes in the Mekong, approximately 205 fish species are known below the Khone Falls and just under 200 species known above the Falls, many of which are migratory. Scientists have recognized the area as a critical bottle-neck for fish migration throughout the lower Mekong basin. 

The Don Sahong Dam – the second dam proposed for construction on the lower Mekong mainstream – would block one of the main channels in the area that allows for year-round fish migration. Well over 100 species migrate through the Hou Sahong Channel, which is one of the largest channels in the area. Unlike other channels, it is free of waterfalls and large enough to support the year-round migration of big groups of large and small fish. If built, the Don Sahong Dam will entirely block the Hou Sahong Channel, endangering fish migration throughout the Mekong region, jeopardizing food and livelihood security in Laos, Cambodia, Thailand and Vietnam.

Despite being less than two kilometers upstream from the Cambodian border, no transboundary impact assessment has been carried out for the project. While the Environmental Impact Assessment (EIA) acknowledges the importance of the Hou Sahong Channel for fish migration, it does not look beyond the borders of Laos to address regional fishery implications.

The project is heavily reliant on the success of proposed mitigation measures which include re-engineering the channels on either side of the Hou Sahong and diverting more water to replicate the characteristics of Hou Sahong, in order to attract fish to migrate up these alternate channels. However, the proposed mitigation measures have never been tested in the Mekong region. No information on which fish species the project would target for migration has been publicly shared, and the details behind the engineering design has not been explained. Experts fear these channels could fail to mitigate the loss of the Hou Sahong Channel for fish migration, not only because the design is untried but because the developer’s assessments fail to take into account the diversity of fish species in the area, each with their unique characteristics and migration patterns. With insufficient baseline data about which species migrate up which channels and when, it is impossible to measure what the true impact of the Don Sahong Dam will be.

It is not clear who will be responsible if the project’s proposed mitigation measures fail. What is clear is that millions of people whose lives depend on Mekong fisheries will bear the brunt of this ill-conceived project, not be the Lao Government or project developers, Mega-First.

An evaluation of the potential impacts of mainstream hydropower dams on Mekong fisheries published by the Mekong River Commission Secretariat in 1994 describes Siphandone as “an ecologically unique area that is essentially a microcosm of the entire lower Mekong River,” and stated that “such a site is so rare in nature that every effort should be made to preserve all of Khone Falls [Siphandone] from any development.”

The Governments of Cambodia and Vietnam have expressed strong concern over the potential impacts of the Don Sahong Dam, and have called for a moratorium on all dam building on the lower Mekong mainstream for a period of 10 years. The Don Sahong Dam is currently undergoing a regional consultation process, despite the fact that construction has already begun. Yet it is not too late to stop this disaster in the making.

More information: 
  • Mekong Governments are expected to meet in January, at the close of a six-month consultation process for the project, to decide the future of the Don Sahong Dam. Take action now to call on Mekong leaders to stop gambling with the future of the Mekong River and her people and cancel the Don Sahong Dam! Sign the petition at
Tuesday, December 16, 2014