Mal jumps into the pool and icy-cold freshwater immediately hits her like a runaway cart, threatening to steal her breath. It can't be more than forty or fifty degrees, and likely originates from some underground stream that hasn't seen the light or warmth of the day in a long time. The weight of her armor immediately drags her down, her thoughts drifting to consider how difficult, likely impossible really, it would be to swim back to the surface if her companions were to drop the rope.
From above a bright light, different and more harsh than the warm tones of a lantern or torch, suddenly shines down on her, though where it comes from she cannot guess, and can only hope that if it's a sign of danger, the others above can handle it and still maintain hold on her only tether to the surface.
The blurred forms of Luban and the slain crayfish both seem to float in suspension as she passes by with only a brief glance. Then, her gaze focused on the depths below, just as the strange light from above starts to fade and disappear again, Maloria notices through her blurred vision, the shine of reflected light glittering upwards at her from maybe 20' feet below. Then darkness. Moments later her boots land in the soft sediment at the bottom of the pool and she feels the tug of a current of cold water rushing past her, confirming that the pool's source is some underground stream. Feeling around, it doesn't take long for her fingers to find a boot, and then Mal's got hold of Thurig, noticing that his body is slowly being dragged away in the direction of the current's flow, not so strong as to require much effort on Mal's part to keep hold of him, but had she not immediately dived in after him, he likely would have been dragged away in short time to wherever the underground stream leads.
Once she has a good hold of the unconscious dwarf, she gives a tug on the rope.