I'd like to add something, if I may.
The carrying capacity of any environment is the area's capacity to repair itself, to regenerate, to protect itself in the long term. It's the environment's capacity not to die.
If the environment is under too much pressure—too many boats, too much gas, too much phosphorus—the life environment dies. The carrying capacity metric is meant to ensure that the environment's ecology can return to normal, heal and renew itself by the following year. That is the idea behind a lake's carrying capacity. It's not just the number of boats. It's also the environment's capacity to return to its natural state.