The Geography of Cambodia: A Land of Rivers, Mountains, and Rich Natural Heritage

Cambodia spans an area of 181,035 square kilometers, situated in the southwestern region of the Indochina Peninsula. Located entirely within the tropics—just over 10° north of the Equator—Cambodia enjoys a warm, humid climate ideal for agriculture, which covers around 20% of its land. The capital, Phnom Penh, sits at the heart of the country, where three major rivers converge: the Mekong, Tonle Sap, and Bassac.

Borders and Regions

Cambodia shares international borders with Thailand and Laos to the west and north, and Vietnam to the east and southeast. It is also bordered by the Gulf of Thailand to the south. Administratively, the country is divided into 20 provinces, 2 municipalities, 172 districts, and 1,547 communes. Three coastal provinces have access to a 435-kilometer-long coastline, known for its mangrove forests—some of which remain largely undisturbed.

Key Geographical Features

One of Cambodia’s most defining natural landmarks is Tonle Sap Lake, the largest freshwater lake in Southeast Asia. It sits at the center of the Tonle Sap Basin-Mekong Lowlands, a vast, low-lying region with elevations typically under 100 meters. This region is surrounded by mountain ranges and plateaus that form natural borders and eco-regions:

• Cardamom Mountains (southwest): Rising over 1,500 meters, with Phnom Aural as the highest peak at 1,771 meters.
• Elephant Mountains: An extension of the Cardamom range, reaching heights of 500 to 1,000 meters.
• Dangrek Mountains (north): Forming a natural boundary with Thailand, averaging 500 meters in elevation, with some peaks above 700 meters.
• Ratanakiri Plateau and Chhlong Highlands (east): These highlands connect with Vietnam’s Central Highlands, forming a rugged and forested landscape.

The Mekong River and Tonle Sap System

The Mekong River, flowing from north to south, plays a crucial role in Cambodia’s hydrology. Passing through a tropical wet and dry zone, it brings about 80% of its annual rainfall during the southwest monsoon (May to October). The Mekong’s flow at Kratié averages 441 cubic kilometers per year, or 93% of the total discharge into the sea.

A unique phenomenon occurs in the Tonle Sap River, a 120-kilometer waterway connecting the lake to the Mekong. During the rainy season, floodwaters from the Mekong reverse the flow of the Tonle Sap River, sending water back into the lake. This expands Tonle Sap Lake from 2,600 km² to 10,000–13,000 km², raising its water level by an average of 7 meters—earning Tonle Sap the nickname of the “world’s only river with a natural reverse flow.”

Ecological Significance and Flood Regulation

This seasonal reversal turns Tonle Sap into a natural flood retention basin, absorbing monsoon floods and releasing water during the dry season. This process contributes up to 16% of the Mekong’s dry-season flow, helping to combat salinity intrusion in Vietnam’s lower delta. It also leaves behind rich sediment layers and rejuvenates the flooded forest zone, which supports one of the world’s most productive inland fisheries. Sadly, these forests are under threat from deforestation and land conversion.

The floodplain surrounding Phnom Penh and extending toward Vietnam covers approximately 7,000 km², playing a critical role in flood control, biodiversity, and agriculture.