An understanding of the Tonle Sap Lake is essential before it is possible to describe the nature of the floating villages that The Lake Clinic serves. The Tonle Sap Lake, known also as the Great Lake, lies in the central plains of Cambodia (Figure 1.1). Its size varies from approximately 160 km long and 35 km wide during the dry season up to 250 km long and almost 100 km wide at the height of the flooding. The water levels rise in most part due to the surging of water coming south from the Mekong River. So much water, in fact, that it causes the Tonle Sap River to reverse its flow and fills in the Tonle Sap Lake. Cambodia’s own rainy season then adds yet more volume to the already swelling lake. In maps, the Tonle Sap Lake is usually presented during the dry season when the lake is its smallest. The Tonle Sap River connects the lake to the Mekong River and joins it at Chaktomuk junction near Phnom Penh, after which the river immediately splits into the smaller Bassac River and the larger Mekong River (Lamberts 2001).