Which example illustrates the tragedy of the commons?

The tragedy of the commons refers to a situation in which individuals, acting in their own self-interest, deplete shared resources, leading to negative consequences for the entire community. The example of multiple fishers over-exploiting a river's fish supply perfectly illustrates this concept. Each fisher seeks to maximize their catch without regard for the overall fish population, ultimately resulting in overfishing. As the fish become scarcer due to excessive harvesting, all fishers face declining returns, demonstrating how collective individual actions can lead to resource depletion.

In contrast, the other options do not encapsulate the essence of the tragedy of the commons. An overpopulation of farms in urban areas could indicate land use issues but does not specifically highlight shared resource depletion. Excessive land use for agricultural purposes suggests unsustainable practices but again does not focus on the collective action problem inherent in the tragedy of the commons. Stable fishing practices among local communities represent a successful management of shared resources, which is the opposite of what the tragedy of the commons entails. Hence, the correct answer underscores the fundamental idea of individual overuse and its consequences on a shared resource.