"It's called the Black Lake," Jezzabelle said raising her hand. "And it was probably named that because it goes down pretty deep so you can't really get a good filtration of light. Or there could be an enchantment on the lake that makes it black, which would hide the creatures below so that, if the school were under attack, the attackers wouldn't see the creatures below." That was one big speculation as to why the lake was called the Black Lake.