I will not say that this happened, this is merely a hypothesis.
If it had happened, if it had happened that close on a dozen girls had skinny dipped in the lake, in a place remarkably close to the centre of a seaside town… if they had, they might have found that the cover of darkness is quite exceptional, the bright lights being all around, but not actually in that place. If they had, there would only have been the squealing of delight to give them away. They would have been invisible, but not, it is true, inaudible. But the Outside is a big place, and giggling would have carried only so far. The Outside is good for swimming.
If they had swum there. Hypothetically.