The Tonle Sap: Southeast Asia's largest freshwater lake explained
The Tonle Sap grows several times its dry-season size each year, feeding millions of people. Here's how the lake works, why it matters and how to see it.
In this guide
The Tonle Sap is the beating heart of Cambodia. This great lake in the centre of the country expands and contracts with the seasons, feeding one of the world's richest inland fisheries and supporting floating and stilt villages around its shores. It is generally described as the largest freshwater lake in Southeast Asia.
A lake that breathes
In the dry season, the lake is relatively shallow and covers a smaller area. When the monsoon rains arrive and the Mekong swells, water flows up the Tonle Sap river into the lake. By the end of the rainy season, the lake's surface area can grow several times larger and its depth increases dramatically, flooding the surrounding forests and fields.
As the rains ease, the flow reverses and the lake drains back towards the Mekong. This annual pulse is what makes the ecosystem so productive.
Why it matters
- Fish: the flooded forests provide breeding and feeding grounds for many fish species. Fish from the lake are a major source of protein for Cambodians.
- Farming: the retreating water leaves fertile soil for rice and vegetables.
- Wildlife: the floodplain is home to large waterbird colonies, including storks, pelicans and cormorants.
- People: hundreds of thousands of people live around the lake, many in villages built on stilts or floating on the water.
The lake as a UNESCO biosphere reserve
The Tonle Sap has been recognised by UNESCO as a biosphere reserve, with core areas such as Prek Toal protected for wildlife.
Threats
Researchers and communities are concerned about overfishing, the clearing of flooded forests, changes in rainfall and the effect of dams on the Mekong's flow, which could weaken the annual flood pulse that the lake depends on.
How to see the Tonle Sap
- From Siem Reap: stilt villages such as Kampong Phluk and Kampong Khleang, and the Prek Toal bird sanctuary.
- From Battambang or Pursat: quieter floating villages such as Kampong Luong.
- From Kampong Chhnang: floating communities and pottery villages near the lake's southern end.
Choosing a tour
Some Tonle Sap tours, particularly to the most visited village near Siem Reap, have a reputation for high prices and pressure to make donations. Book through reputable operators, agree the price in advance and choose tours that benefit the local community.
Best time to visit
The rainy and early dry season (around August to December) is when the villages are surrounded by water and the flooded forests are reachable by small boat. In the late dry season, water levels can be low and some areas are hard to reach.