They were behind the Crystal Caverns and marked the entrance to the caves of the white trogs. The White Trogs used the Drowning Pools as a trap to hunt for food and intruders. When one entered the Crystal Caverns, the Trogs were alarmed by the soft vibration and eerie sound of the crystals. An intruder then got caught in a spider's web, activating the trap. A boulder rolled towards him. The intruder, naturally, began to run towards the next cave which the boulder would close. The drowning pools then were filled with water by the geysers, and when the victim was dead, the trogs entered the cave via a secret mechanism hidden in a stalagtite. Blatch Helmstoft was the first to discover the Drowning Pools and discovered the trap but was nevertheless caught in it.