The Mekong Delta is the flat, river-built lowland of southwestern Vietnam where the Mekong splits into distributaries and reaches the sea, the East Sea (South China Sea) on one side and the Gulf of Thailand on the other. It covers more than 40,500 km², from Châu Đốc and Hà Tiên near the Cambodian border down to Cape Cà Mau at the southern tip of the mainland, and most of it is rice paddy, orchard and canal laid over a seasonally flooded plain with a mean elevation of only about 0.82 metres. What survives of its wild habitat lies in a handful of reserves: Tràm Chim National Park, a Ramsar site since 22 May 2012, which protects the sarus crane; the peat swamp of U Minh Thượng National Park (2002); and the mangroves of Mũi Cà Mau National Park, which became a Ramsar site on 13 April 2013 and is part of a UNESCO biosphere reserve.
The delta has been called a "biological treasure trove"; more than 1,000 animal species were recorded in the region between 1997 and 2007. Yet forest covers only about 300,000 hectares, or 7.7% of the land (2011), the smallest share of any region of Vietnam. The animals that define it are therefore tied to a few named places, and each tells a different part of the delta's story.
Sarus Cranes in the Plain of Reeds: Tràm Chim Since 1986
The emblem of the delta is the sarus crane, the tallest flying bird in the world at up to 1.8 metres, grey with a bare red head and upper neck. The cranes of Vietnam and Cambodia form the species' southern Southeast Asian population, and in the delta their stronghold was always the Plain of Reeds (Đồng Tháp Mười), an inland "back swamp" of acidic soil spread across Đồng Tháp and Long An. In the 18th century the plain covered about 1,000,000 hectares; drainage has since halved it.
During the Vietnam War parts of the plain were drained and burned for military reasons. Once the acid sulphate soils dried out they oxidised and became highly acidic, and fires became more frequent. In 1985 Đồng Tháp province set up Tràm Chim as a forestry and fishery enterprise and began restoring the flood regime. A year later, in 1986, sarus cranes were found there. Protection followed in steps: a provincial reserve in 1991, a national reserve of 7,500 hectares in 1994, and Tràm Chim National Park by government decision on 29 December 1998, with an area adjusted that year to roughly 7,300–7,600 hectares depending on the survey.
Restoration brought back more than cranes. The Bengal florican, a critically endangered bustard with fewer than 1,000 individuals estimated alive in 2017, may still persist at Tràm Chim. The giant barb returned to the park's waters, and so did wild rice (Oryza rufipogon). Vietnamese records list more than 100 vertebrate species, 40 fish species and 147 waterbird species. In 2016 Asian openbill storks nested there as a colony of about a thousand nests, the first such colony in almost 30 years. The cranes themselves have become rare; managing water levels to prevent fires changed the grassland they fed on. Four sarus cranes were recorded back at Tràm Chim in March 2024, an early sign that a crane recovery project and the restored water and fire management are working.
Melaleuca Swamps from Láng Sen to Trà Sư
Before rice took over, much of the inland delta was swamp forest dominated by Melaleuca cajuputi, the cajuput or paperbark tree known in Vietnamese as tràm. These trees tolerate months of flooding and acid soils, and the forests they form shelter water birds, snakes, fish and the insects that feed them. Two of the best surviving examples sit at opposite ends of the upper delta.
Láng Sen Wetland Reserve, in the Long An part of the Plain of Reeds, covers 5,030 hectares and became a wetland reserve by government decision in early 2004, after surveys that began in 1998. Preliminary counts found 156 wild species and 149 vertebrate species, 13 of them in Vietnam's Red Data Book, and the reserve was one of two Mekong Basin sites chosen by IUCN, the Global Environment Facility and UNDP for a biodiversity programme. Among the new species found there is a gecko with bright orange legs, a yellow neck and a blue-grey body.
In An Giang, near the Cambodian border, the Trà Sư cajuput forest shows what this habitat looks like in the flood season: rows of pale trunks standing in water carpeted with duckweed, threaded by boat channels. An Giang and Cà Mau together hold about two-thirds of all forest left in the delta; in every other province forest covers less than 5% of the land.
Hairy-Nosed Otters in U Minh Thượng's Peat Swamp
Further southwest, in the old Kiên Giang province near Rạch Giá, lies the U Minh forest, a peat swamp that was a Viet Minh and later Viet Cong base. Its northern part became U Minh Thượng National Park by Decision 11/2002/QĐ-TTg, signed on 14 January 2002, and covers about 80.53 km². It is generally considered the richest part of the delta for plants and animals: 243 plant species, 32 mammal species, 187 bird species, 39 amphibians and 34 fish.
The park's most important mammal is the hairy-nosed otter, one of the rarest otters in the world. Camera traps recorded it at U Minh Thượng in 2000, and droppings with fish scales and crab remains were found there; in 2008 it was also recorded in U Minh Hạ National Park to the south. Both reserves are peat swamp forests ringed by Melaleuca up to 15 metres tall, crossed by canals full of water hyacinth and water lettuce, and buffered by rice paddies. The bird list includes the oriental darter, spot-billed pelican, black-headed ibis, glossy ibis, greater spotted eagle and Asian golden weaver.
U Minh also shows what has already gone. Both the saltwater crocodile and the Siamese crocodile once lived in the swamp, but a 2002 study concluded that both were extinct in the park. The Siamese crocodile's world population has fallen by more than 80% since the 1940s, and only small groups survive in Vietnam.
Mangroves and Mudflats at Mũi Cà Mau
At the delta's southern point, in Đất Mũi commune, the land ends in mangroves and mudflats where the Gulf of Thailand meets the open sea. Mũi Cà Mau National Park was established on 14 July 2003 from a nature reserve first set up in 1986. It covers 41,862 hectares: 15,262 hectares of land and 26,600 hectares of coastal water. UNESCO added it to its list of biosphere reserves on 26 May 2009, and in 2013 it became the world's 2,088th Ramsar site.
Fish dominate the species list because the mangrove roots and mudflats act as a nursery for both river and sea fish. The mangroves also defend the coast: they are a natural barrier against storms and erosion for the low-lying delta behind them. That role is under strain. Between 1973 and 2005 the growth of the delta's seaward shoreline slowed from an average of 7.8 metres a year to 2.8 metres; after 2005 it began to retreat at about 1.4 metres a year, and the delta as a whole switched from gaining land to losing it. An embankment was built at Cape Cà Mau in 2012 to stop landslides, and the park plans to replant about 150 hectares of mangrove by 2025.
The cause lies largely upstream. The river still carries more than 160 million tonnes of sediment a year, including 6.5 million tonnes of sand, but historic loads were higher, and dams in the upper basin and sand mining in the riverbed have cut the supply that once built the delta outward. A 2019 study in Nature Communications measured the delta's mean height at 0.82 metres above sea level, with 75% of it, home to about 12 million people, below one metre.
Giant Catfish, Giant Barb and 58% of Vietnam's Fish
The delta's most numerous wild animals are under water. The Mekong system has the second-highest aquatic biodiversity of any river after the Amazon, and the Greater Mekong region holds an estimated 850 freshwater fish species. No other river has so many very large fish: the Mekong giant catfish, giant pangasius and giant barb can each reach about 3 metres and 300 kg. All have declined sharply, and the Irrawaddy dolphin, once common throughout the lower Mekong, is now down to about 85 individuals.
The fish also feed the delta's economy. Around 2011 the region produced 3.168 million tonnes of fish and seafood, 58.3% of Vietnam's total, with two-thirds of it from aquaculture rather than the open sea. Much of that farming is of Mekong catfish, above all the iridescent shark (Pangasianodon hypophthalmus), sold abroad as pangasius or basa; Vietnam's pangasius exports reached US$1.8 billion in 2014. The same paddies also produced 23.2 million tonnes of rice in 2011, 54.8% of the national harvest. That makes the wildlife reserves islands in one of the most intensively farmed landscapes in Asia, and their survival depends on how the river's water, sediment and salt are managed in the years ahead.
The delta's wildlife is shaped by events far upstream, so it helps to follow the river from Tibet in our complete guide to the Mekong River, and to look at the great Cambodian flood lake that feeds the delta in the dry season in our guide to the Tonle Sap wetlands. For the monsoon rhythm that floods the Plain of Reeds each year, see the climate of Vietnam.