Is there a term for swimming in a lake WHILE it's raining outside?

I don't know, but my dad always said that you shouldn't swim in the rain...you'll get all wet.

Yes indeed. The technical term for such an activity is "fun".

I remember one time swimming in a council pool when the rain was lashing down and there was a gale-force wind  blowing from the south. I had the pool to myself and if swimming the north-bound laps was fun, coming back was like swimming in the surf as the wind whipped up the surface.

It was a very small surf, I know, but it was an experience I'll never forget. Just good fun.

That depends, is there lightning with the rain? If so, foolish. If not, redundant.