Lake Thulu was a lake located near the Tower of Erebus. Erebomancy practiced in the tower had strange side effects on it, which created an effect somewhat similar to water pollution. It was polluted so much that even Mud Dragons weren't able to live there, the only inhabitants were Ooze Dragons. During the Cataclysm, the Scar of the World was created an opened up on the place the lake once layed, destroying it. When the Ooze Dragons later came back, they settled in The Aichpey River instead.