Kennedy thought of the question. If the castle was in fact 1,000 years old then the lake might of have been useful for many things other than housing merpeople and gryndylows... and possibly other creatures. He raised his hand and said, "The lake could have been included for many reasons, some may be that the founders wanted the castle to have a close water supply." You know because the pipe system wasn't invented yet 1,000 years ago...maybe.

"It could also be that there are plants growing under the lake that could be useful for Herbology," but this wasn't Herbology class, "Or maybe the lake holds creatures that aren't found on land and the founders thought they would be good for educational purposes." He was thinking this in a different way, but at least he was answering the question.