The RIVER BASIN GAME is a dialogue tool for decision makers and water users tested in Tanzania and Nigeria. It comprises a physical representation of a river catchment. A central channel flows between an upper watershed and a downstream wetland and has on it several intakes into irrigation systems. Glass marbles, representing water, roll down the channel. Participants place sticks to catch the marbles and scoop them into the irrigation systems. The players become highly animated and learn that being at the tail end leads to water shortages. The game promotes mutual understanding of a catchment, factors controlling access to water, conflict dynamics and allows participants to react to scenarios. By drawing from their own and outsiders' knowledge, players explore solutions to redistributing water. We examine the RIVER BASIN GAME as a metaphor, proposing that it has a mix of simplicity and realism that encourages players to understand issues of real-world complexity and scale. We suggest that the game's success is related to its quality of metaphor, influenced by organizational factors and by six game and gaming experiential axes each with two polarities: seriousness and play, accuracy and generality, internality and externality, connection and disconnection, individualism and collectivism, rule following and rule breaking. (Contains 4 figures and 2 tables.)