Mekong

The Mekong (ទន្លេមេគង្គ) is the great river of mainland Southeast Asia. Its basin reaches about 4,500 kilometers (2,800 miles) from the Tibetan Plateau to the South China Sea. In Cambodia it carries fish, boats and floodwater past Phnom Penh, where it meets the river of the Tonle Sap (ទន្លេសាប), and it is home to the country's last river dolphins. The name comes from Mae Nam Khong, "mother of water".

Phnom Penh across the water where the Mekong meets the Tonle Sap River, 2026. Photo: Josep Renalias, CC BY 4.0

Place details
Khmer name	ទន្លេមេគង្គ
Place type	River
Country	China; Myanmar; Laos; Thailand; Cambodia; Vietnam
Subjects	Land, Place & Environment

Course in Cambodia

The Mekong runs about 480 kilometers (300 miles) through Cambodia, from the border with Laos in the north to Vietnam in the south, and is about 1.5 kilometers (1 mile) wide on average. It passes through the provinces of Stung Treng, Kratie and Kampong Cham, then Phnom Penh and Kandal. Down to Kratie the water runs fast over shallows and is hard for boats; from Kratie to Phnom Penh it is deep and slower, and ships can use it. Below the capital the Bassac River branches off, deep enough for ships of 3,000 tons bound for foreign ports.

In the wet season the river carries about twenty times as much water as in the dry season. Its average flow in Cambodia is 2,860 cubic meters a second, 18 percent of the flow of the whole basin. About a quarter of that water comes from Tibet and China, and about half from northeastern Thailand and Laos.

Funan, one of the first recorded states of Southeast Asia, grew up on the fertile plain of the lower Mekong, which stretches up to Phnom Penh.

Phnom Penh and the Tonle Sap

At Phnom Penh the Mekong meets the Tonle Sap River, a few hundred meters from the city's port. In the wet season, from June to October, the swollen Mekong pushes water up the 110-kilometer (70-mile) Tonle Sap River into the lake. In the dry season, from November to May, the Tonle Sap River runs the other way and drains the lake back into the Mekong.

In 2019 the monsoon rains came late, and the Mekong fell to its lowest level in a hundred years.

Fish

More than 800 species of fish live in the Mekong basin, one of the richest river faunas in the world. The fish biologist Zeb Hogan wrote that one catfish migrates more than 1,000 kilometers and that eight species grow longer than 2 meters (6.5 feet). Hogan put the basin's catch at about 2.5 million tons a year, worth 3 to 6 billion dollars, and wrote that most of the protein eaten by the basin's 60 million people comes from fish. A report in 2024 found that a fifth of the river's fish species assessed are at greater risk of extinction.

Dolphins

The Mekong's last Irrawaddy dolphins live in Kratie and Stung Treng. In Cambodia the dolphin is held sacred. In several tales it was once a woman who leapt into the river to escape being married to a snake.

The dolphins keep to three deep pools, at Koh Pdao, Koh Ro Ngeav and Kampi. The Kampi pool in Kratie, about 60 meters (200 feet) deep and named after the rapids above it, is where more of them have come to spend most of their time. A 2020 census counted 89 adults, against an estimated 200 in 1997. In February 2022 the last dolphin of the Chheu Teal pool, on the border with Laos, was found dead, and the dolphins were gone from Laos. Conservationists told Dialogue Earth that the decline there followed the start of the Don Sahong dam in Laos, about 2 kilometers away, in 2020.

Core zones along 180 kilometers (110 miles) of the river in Kratie and Stung Treng were set up in 2012 to protect the dolphins, and the fisheries department employed 72 river guards in 2022. Electrofishing is banned throughout Cambodia; gill nets are banned only in the core zones, and dolphins drown in them. Longline hooks killed three adult dolphins within a week in December 2022. In February 2023 Prime Minister Hun Sen signed a sub-decree that made 120 kilometers (75 miles) of the river a dolphin protection zone: 35 kilometers in Stung Treng and 85 in Kratie. It bans fishing and fish farming there and limits boats to 30 kilometers an hour. The Irrawaddy dolphin has been listed as critically endangered by the International Union for Conservation of Nature since 2004.

On Mekong River Dolphin Day at Kampi in November 2025, the Ministry of Agriculture, Forestry and Fisheries reported the first full year without a dolphin death since its records began in 2002. It also reported seven newborns, for a total of 111 dolphins. In December a calf about a day old was seen at Kampi, the eighth born that year, bringing the count to 112.

Dams and sand

The Mekong River Commission, set up in 1995, works on the shared management of the basin. Dams proposed at Sambor and Stung Treng on the Cambodian Mekong are politically contested, and decisions on them have been put off over worries about fisheries, the people who would be moved and the effects downstream.

Sand is dredged from the riverbed for building. In the middle of 2015 the Ministry of Mines and Energy began auctioning licenses to mine sand at Roka Koang in Kandal, about 45 kilometers (28 miles) upstream from Phnom Penh. Cambodia banned sand exports in 2017 and lifted the ban in 2020. In 2022 the ministry counted 49 licenses covering 2,320 hectares of the Mekong and Bassac, and reported 11.7 million cubic meters of sand taken in 2020 and 11.5 million in 2021. Residents of Roka Koang told Mongabay that the mining caused the riverbank collapses that took their land. The government holds that the collapses are natural, while a peer-reviewed study published in 2020 linked heavy sand mining to unstable banks.

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