Salween Estuary
The Salween Estuary is the final section of the Salween River, which is the longest river in Myanmar (Burma). Originating in the Tibetan mountains, the river flows through narrow gorges before entering the Gulf of Martaban, where it merges with the Ataran and Gyaing Rivers to create an alluvial delta. Known by various names in different regions—such as Thanlwin in Burma and Nu Jiang in China—the Salween is primarily navigable only for a short distance and has historically been significant for transporting teak logs. In recent years, environmental changes due to climate impacts, such as altered glacier melt and monsoon patterns, alongside dam construction, threaten the river's flow and ecological balance.
The estuary supports a rich biodiversity, including around 140 species of fish and various turtles, while the surrounding wetlands serve as crucial habitats for numerous local species and fisheries. However, human activities, such as agricultural expansion and deforestation, have transformed the landscape, diminishing the original biodiversity. The interplay of freshwater and saltwater in the estuary is vital for local ecosystems, but rising sea levels and additional dam projects raise concerns about increased salinity and habitat loss. The future of the Salween Estuary will likely depend on collaborative efforts across national boundaries to address these environmental challenges effectively.
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Salween Estuary
Category: Marine and Oceanic Biomes.
Geographic Location: Southeast Asia.
Summary: Where one of southeast Asia’s major rivers meets the Andaman Sea, a rich wetland ecosystem is threatened by dam construction and other human activity.
The Salween Estuary is the lowest segment of the longest river flowing through Burma (Myanmar). The Salween descends through narrow gorges from the Tang-ku-la Mountains of eastern Tibet, China, to the Andaman Sea, entering the Gulf of Martaban at Moulmein, where it joins the Ataran and Gyaing Rivers to form an alluvial delta. The Salween is known by many names, depending upon the location: in China, the Nu Jiang or Nu; in Burma, Thanlwin; in Tibet, Gyalmo Ngulchu, to name a few. The river is traversable by boats only for a comparatively small distance, and its principal economic role has been as a conduit for teak logs to be floated downstream for manufacturing and export.
![Asian Pond Terrapin. By Sandeep Gangadharan (Flickr: Indian Black Turtle) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons 94981613-89723.jpg](https://imageserver.ebscohost.com/img/embimages/ers/sp/embedded/94981613-89723.jpg?ephost1=dGJyMNHX8kSepq84xNvgOLCmsE2epq5Srqa4SK6WxWXS)

The regular flow of the river, and its contribution to balancing the saltwater in the estuary, has been threatened in recent years by climate change impacts on the Tibetan and Himalayan seasonal glacier melt and on monsoon rains—predictable patterns of each have been altered—as well as the construction of hydroelectric dams upstream. In the twenty-first century, conflict between the central government of Burma and ethnic minority groups seeking autonomy, particularly the Karenni, has hampered the construction of some infrastructure projects, while environmental concerns have become entangled in the political struggles. However, the estuary itself was spared the worst of the damage inflicted by the 2008 cyclone Nargis, the deadliest natural disaster in Myanmar’s history. Nargis left almost 140,000 people dead in its wake.
Political secrecy and cultural chaos in the region mean that accurate figures for water flow and sediment discharge through the Salween Estuary are not entirely satisfactory. However, various historic studies had placed the Salween as among the 20 largest in the world in each category. Some contemporary research indicates the estuary carries and deposits a highly organic yield; this is consistent with the monsoonal climate, the river’s relatively narrow floodplain and limited catchment area, few tributaries, and the presence upstream of extensive forested areas on steep slopes.
This heavy organic content has contributed to the absence of seagrasses in the Gulf of Martaban, as is also the case with the delta of the Irrawaddy, Burma’s other major river delivering a heavy sediment load. The Salween Estuary area has daily tides and seasonal flows marking the meeting of freshwater with the saltwater of the Andaman Sea.
Biodiversity
The Salween Estuary is home to approximately 140 species of fish and a diverse range of turtles, including the giant Asian pond terrapin and the bigheaded turtle. Mammals found in and around the wetlands here include the fishing cat, Asian small-clawed otter, and Siamese crocodile. The golden eye monkey, small panda, wild ox, and wild donkey are also found in the Salween floodplain. Plants of the biome include Dendrobium fytchianum, a rare white orchid discovered in the late 1800s and prized among collectors. On the whole, the estuary supports considerable biodiversity, and offers nutrition and income-generating opportunities for numerous local inhabitants.
The estuary receives much of the sediment carried by the Salween prior to its ultimate deposition in the sea. This contributes to the fertility of the area. Beaches and mudflats in the estuary are important feeding and spawning grounds for birds and a variety of fish, crabs, squid, and prawns, which are fundamental to the food web, as well as vital to local fisheries both for domestic consumption and, potentially, future export. Approximately one-third of the fish species in the Salween as a whole are endemic, meaning found nowhere else; many of these range into the estuary.
Effects of Human Activity
The Salween Estuary joins the Irrawaddy Estuary, their deltas, and the region’s coastal rainforests in forming the Burmese coastal ecozone, which also extends to parts of the Bangladesh coastline. Most of this area has already been transformed by making it more practical for agricultural and aquaculture uses. As a result, much of the original lowland swamps and evergreen forest have been cleared, as have the deciduous dipterocarp, montane evergreen, and mangrove forests around the mouth of the Salween.
Inevitably, this has already affected biodiversity in the estuary, which historically supported one of the most diverse systems in the country. Rice plantations, for example, have spread monoculture-dominated vegetation communities across much of the area. Some nonnative species have taken advantage of the invasive opportunities this presents. Global warming and its concomitant sea-level rise means the estuary may become more highly saline further upstream—a trend that damming will only accelerate. By blocking sediment flows, the dams will also make more difficult the restoration of wetlands that will be eroded by sea-level rise and damaged by saltwater intrusion.
These human actions have also affected the long-term flow of sediment into the comparatively shallow Gulf of Martaban, especially since upland forests have also been cleared and replaced by bamboo plantation forests. The extent to which these changes will magnify if several planned major dams are built upstream is not fully clear, but it is evident that because much of the river passes through Chinese territory and in part forms the border with Thailand, the challenges and solutions will require transboundary participation.
Bibliography
American Orchid Society. “Collector’s Item: Dendrobium fytchianum Bateman ex Rchb.f.” 2012. http://www.aos.org/Default.aspx?id=167.
Bird, M. I., R. A. J. Robinson, N. Win Oo, M. Maung Aye, X. X. Lu, D. L. Higgitt et al. “A Preliminary Estimate of Organic Carbon Transport by the Ayeyarwady (Irrawaddy) and Thanlwin (Salween) Rivers of Myanmar.” Quaternary International 186, no. 1 (2008).
Clarke, J. E. “Biodiversity and Protected Areas: Regional Report.” Regional Environmental Technical Assistance 5771 (2011).
Meade, Robert H. “River-Sediment Inputs to Major River Deltas.” In John D. Milliman and Bilal U. Haq, eds., Sea-Level Rise and Coastal Subsidence: Causes, Consequences, and Strategies. Dordrecht, Netherlands: Kluwer Academic Publishers, 1996.
Mon Youth Progressive Organization (MYPO). In the Balance—Salween Dams Threaten Downstream Communities in Burma. Yangon, Burma: Salween Watch, 2007.
Yang, Fan. “Hydrological Characteristics and Changes in the Nu-Salween River Basin Revealed with Model-Based Reconstructed Data.” Journal of Mountain Science, vol. 18, 2021, pp. 2982–3002, doi.org/10.1007/s11629-021-6727-1. Accessed 2 Sept. 2022.