Since the discovery of the Angkor civilization on the shorelines of the Tonle Sap Lake, it has been assumed that rivers played an important role in the establishment of this polity. However, rivers have largely been ignored in previous academic research, which has seen stronger focus on land remains. This has resulted in a biased interpretation of the data, favouring approaches that recognise Angkor as an agrarian state. While the role of agriculture is certainly of great importance, novel research conducted during my doctoral studies suggests that the presence of nomadic fishing communities played a key role in the establishment of Angkor. These communities provided the necessary man-power to capture fish during the short fishing season, which coincided with the rice harvest. These fishing communities had to travel hundreds of kilometres annually to the Tonle Sap Lake following fish migration patterns, while at the same time land-based communities travelled to the lake to obtain the fish needed to produce prahok, a fermented fish paste that is at the heart of Khmer cuisine. This gathering provided opportunities for human interaction and likely acted as a conduit for culture dispersal and knowledge transfer. In this context of cooperation determined by ecological pressure, the only way to understand the complex relationship that emerged from it is by studying how the functional aspects of the environment influenced the cosmological, economic, and political world of Angkor.