Which lake do you want to swim in?

If you have to choose between dirty and clean, it seems like you'll definitely go with clean, right?

What will happen if everyone who wants to swim swims in it?

Will it stay clean?

So a person with good intentions ends up being used as a lake. Without evil intent, "I was passing by, and there's a clean lake, why not take a swim"

The cleanest lake is hidden on the mountain tops, where the weather changes abruptly, and the paths, if they are trodden, are overgrown.

Local residents come to the truly clean lake to perform ritual ceremonies.