Tonlé Sap, commonly translated to "Great Lake" refers to a seasonally inundated freshwater lake, the Tonlé Sap Lake and an attached river, the 120 km (75 mi) long Tonlé Sap River, that connects the lake to the Mekong.

They form the central part of a complex hydrological system, on the Cambodian floodplain covered with a mosaic of natural and agricultural habitats that the Mekong replenishes with water and sediments annually.

The Tonlé Sap Lake occupies a geological depression of the vast alluvial floodplain in the Lower Mekong Basin. The lake's size, length and water volume varies considerably over the course of a year from an area of around 2,500 km2 and a length of 160 km at the end of the dry season in late April to an area of up to 16,000 km2  and a length of 250 km as the Mekong maximum and the peak of the South-West monsoon's precipitation culminate in September and early October.

As one of the world’s most varied and productive ecosystems the region has always been of central importance for Cambodia's food provision. It proved capable to maintain the Angkorean civilization, the largest pre-industrial settlement complex in world history.

Either directly or indirectly it affects the livelihood of large numbers of a predominantly rural population to this day. With regards to a growing and migrating population, ineffective administration and widespread indifference towards environmental issues the lake and its surrounding ecosystem is coming under increasing pressure from over-exploitation and habitat degradation, fragmentation and loss.  The largest freshwater lake in Southeast Asia, that contains an exceptional large variety of interconnected eco-regions with a high degree of biodiversity is a biodiversity hotspot and was designated as a UNESCO biosphere reserve in 1997. That does not mean that you can drink the water!

I visited a floating village close to Siem Reap, where evidence of tension between the cambodian and vietnamese people settling (invading?) the lake are evident. The dramatic sky was due to a heavy tropical storm that swept in while visiting.