In June and November the Tonle Sap River changes
direction. In June, with monsoon rains swelling the Mekong, excess water is
pushed into the Tonle Sap that then drains back upstream into the lake, flooding
the surrounding low plains. By monsoon's end, in November, the pressure is
relieved and the Tonle Sap reverses course and returns to the direction of flow
expected of it.
However, the waters of this, the largest of Southeast Asian lakes, take several more months before they begin to recede, and it is not until February that Tonle Sap Lake begins its return to normal size. The mud banks created by the flooding are extremely fertile, and local rice farmers have developed a deepwater rice that is unique to this area.
The months of flooding also encourages the growth of huge fish stocks and other aquatic life, that become extremely easy to catch once the waters begin to reside. Fishing families string nets and bamboo traps across the lake's mouth and the numerous fish can almost be plucked from the water. The Tonle Sap Lake's level drops so fast that it catches out many of its inhabitants, and it is not unlikely to see fisherman picking their catch from the trees.
One particularly interesting lake dweller is the Elephant Fish, which has developed the ability to last for several hours out of water, in case the fast receding waters leave it stranded in the mud. This fish is an Asian delicacy and can fetch as much as US$60 in a Singapore restaurant.
By the end of May the lake has returned to its original size - just in time for the June monsoons to turn the tide of the waters all over again.