Abstract: Tonle Sap Lake is the largest lake linked with Mekong River. The variations of water level and area exert vital impact on the structure and function of Tonle Sap Lake. Identifying the evolvement rule of water level and area is of guiding significance for flood control and drought relief as well as eco-environmental protection in Tonle Sap Lake and the Mekong Delta. According to long series of daily water level data of Phnom Penh Port, Prek Kdam and Kampong Luong stations and topographic data of lake area, we analyzed the inter-annual and annual variations of water level and area of Tonle Sap Lake. Results reveal that the water level of Tonle Sap Lake raise and fell slowly, with the rising duration shorter than falling duration and rising rate higher than falling rate. The water level of Tonle Sap Lake fluctuated frequently between years, with the annual average water level, annual maximum water level, annual water level range, annual flood duration, annual average flood level and daily rising rate all showing slight downward trend, while the annual lowest water level, water withdrawal days and daily falling rate showing upward trend. The annual water level and area of Tonle Sap Lake changed with a single peak value. The lowest water level was in May, when the average water level was 1.51 m and the corresponding area 2 487 km², the measured minimum water level 1.11 m and the corresponding area 2 053 km²; the water level reached the maximum value in October, when the average water level was 8.70 m and the corresponding area 12 768 km², the measured maximum water level 10.54 m and the corresponding area 15 261 km². Multi-year average water level range of Tonle Sap Lake was 7.63 m and the corresponding area range was 10 628 km².

Key words: water level, area, variation characteristics, ecological environment, Tonle Sap Lake