A classroom experiment that can be used to teach students why society overuses commonly owned resources.Students play the role of fishermen who must decide how many fish to catch. Initially each student catches fish in their own privately owned lake and most will quicly choose a sustainable catch. In the last session all students fish in the same large lake, and the usual result is overfishing that destroys the fish population. The central point of the game is the importance of private property rights. It also illustrates the difficulties of maintaining cartels, the welfare of current versus future generations, and the political difficulties with solving the problem of overfishing. Finally, it demonstrates that economics is relevant to understand current public policy issues. The document includes references to several news articles about overfishing that can be assigned before or after the experiment.