Oregon lake has a drain hole at the bottom but also has water flowing into it. Pingualuit crater has no water flowing into it but probably has no drain hole at the bottom either.
I'm wondering if there's also a lake that has no water flowing into it but has a drain hole at the bottom. If such a lake exists, would the water in it be very pure because the slightest bit of impurities in it move to the drain hole and flow out? I think that for such a lake to exist, the land around it would have to be higher than the land further away like Pingualuit crater.