Six Countries, One Long River
The Mekong starts high on the Tibetan Plateau and ends about 4,909 km later in the South China Sea. That makes it the world's twelfth-longest river and the third-longest in Asia. Every year it pours out about 475 cubic kilometres of water. In its upper 2,200 km, it drops 4,500 metres, much of the way through narrow, deep gorges.
On the way, it passes through China, Myanmar, Laos, Thailand, Cambodia and southern Vietnam. In China it has an official name of its own, the Lancang River. For long stretches it also works as a border. It splits Laos from Thailand for hundreds of kilometres.
The name hides a small joke. In Thai and Lao, big rivers are called Mae Nam, meaning "Mother of Water". Khong is an old word that simply meant "river". So "River Khong" really means "River River". In Khmer, people also call it Tonle Thum, the "Big River".
The River That Turns Around
At Phnom Penh in Cambodia, the Mekong meets a river and lake system called the Tonle Sap. For part of the year, the Tonle Sap behaves like a normal tributary and flows into the Mekong. But when the Mekong floods, the flow reverses. Floodwater pushes up the Tonle Sap toward the largest lake in Southeast Asia.
Further south, things get even stranger. The river's low tide level in Cambodia sits lower than the high tide out at sea. So the flow of the Mekong flips with the tides all through Vietnam and up to Phnom Penh. That makes the flat land there easy to flood. Every rainy season, 35 to 50 percent of this last stretch goes under water.
That flat land is the Mekong delta, and it is young. Its current shape formed over the last 6,000 years, as it pushed 200 km out over the sea floor. At one stage it grew by 17 to 18 metres every year.
A River of Giants
No other river is home to so many species of very large fish. The giant freshwater stingray can reach at least 5 metres long and 1.9 metres wide. The giant pangasius, the giant barb and the Mekong giant catfish can each grow to about 3 metres and 300 kg. That catfish is endemic to the river.
The records back this up. In 2005, a 293 kg Mekong giant catfish was caught in the river, the largest freshwater fish recorded at the time. Then in 2022, a 300 kg giant freshwater stingray took the title.
The basin is packed with life of every size. Only the Amazon has more. Scientists count about 850 freshwater fish species here. Between 1997 and 2015, an average of two new species a week were found in the region. Sadly, many of the giants have declined because of dams, flood control and overfishing. Only 85 Irrawaddy dolphins remain in the lower river.
Dinner From the River
The Mekong basin has one of the largest and most productive inland fisheries on Earth. The lower basin yields about 4.5 million tonnes of fish and other water animals each year. That includes fish raised through aquaculture, plus wild crabs, shrimp, turtles and frogs. Surprisingly, about two thirds of the wild catch comes from flooded rice paddies.
For many families, this is the main meal. In Cambodia, around 80 percent of the protein people eat in a year comes from fish caught in the Mekong system. Fish are the cheapest animal protein in the region, so any drop in the catch hits poor families hardest.
About 40 million rural people take part in the wild fishery. That is more than two thirds of the rural population in the lower basin. In Laos, 71 percent of rural households rely on fishing for food or extra cash. Around Cambodia's Tonle Sap Lake, more than 1.2 million people live in fishing communities.
Too Wild to Sail
Rapids, waterfalls and big swings in water level make the Mekong hard to navigate. Between 1866 and 1868, a French expedition travelled from the river's mouth all the way to Yunnan. Their main finding was a letdown: the river had too many falls and rapids to ever be useful for shipping. Its source was not found until 1900.
People have lived along it for a very long time. At Oc Eo, near the delta, diggers found coins from as far away as the Roman Empire. Today, a deep-water port at Cai Mep in Vietnam can take the largest container ships in the world.
In 1995, Laos, Thailand, Cambodia and Vietnam set up the Mekong River Commission to share care of the river. Dams built for hydropower since the 2000s have caused serious problems for its ecosystem. The Mekong is also one of just 10 rivers that carry 90 percent of the plastic in the oceans.
