Final answer:
The situation described is an example of the tragedy of the commons, where self-interested individuals deplete a public resource. A modern example of this is global climate change.
Step-by-step explanation:
The situation described in the question is an example of the tragedy of the commons.
In the tragedy of the commons, self-interested individuals have incentives to take as much of a public resource as they can, which can lead to the depletion of the resource. In this case, as more people go to the lake, it becomes more congested, making it less enjoyable for Dave to swim.
One modern example of the tragedy of the commons is global climate change, where individuals and countries taking actions that benefit themselves contribute to the overall negative outcome.