Every year in the fall when the Tonlé Sap (the Sap River) reverses its flow, Cambodia erupts into the biggest celebration. For three days in November, the country descends on Phnom Penh for the annual Cambodia’s “thanksgiving festival.” The Tonlé Sap is part of Boeung Tonlé Sap, the lake and river system that stretches across the heart of the country. The French refer to Boeung Tonlé Sap as the Great Lake. The Tonlé Sap links the Mekong to the Great Lake in Phnom Penh, a drain between the two. From May to October when the southwest monsoon brings the rainy season to Cambodia, the Mekong swells. The Mekong rises so fast that not all its water can flow south into the sea. Instead, some of the water forces the Tonlé Sap to reverse its direction, flow north into the Great Lake, and flood its surrounding forest and land. But when the dry season arrives and the Mekong’s level drops, the lake empties its water via the Tonlé Sap back into the Mekong and flows south to the sea. As a result, the Tonlé Sap flows half the time from southeast to northeast and the other half in the opposite direction.

As the largest freshwater lake in Southeast Asia, the Great Lake is a fishery hotspot and one of the largest catches in the world. Its biodiversity is second only to the Amazon. The lake has been sustaining the Khmer race since the beginning. More than 70% of the country’s protein intake comes from the lake. It also feeds our neighbors, who import thousands of tons each year as well. And it’s not just fish, the flooded land surrounding the lake becomes a fertile ground for the country’s rice production. The Great Lake is the rice bowl of the country. The Great Lake plays a vital role in Khmer culture, which is reflected in our belief, cuisine (we eat 140 pounds of fish per capita annually), livelihood and tradition. Its importance can be found on the bas-reliefs of our medieval temples. It is believed that the Khmer Empire would not have grown as prosperous as it did if not for the Great Lake. Angkor, the old capital, sits on the lake’s northwestern shore.