OOC:
Some quick Googling and completely unscientific alanysis would suggest a dwarf weighs about 150lbs, and a set of plate armor would weigh about 50lbs. Furthermore, a powerful wizard named Archimedes, who probably only Eltrezar and Spugnoir would have heard of, once wrote a famous principle stating that a body immersed in a fluid is subjected to an upwards force equal to the weight of the displaced fluid, and therefore 1lb on land weighs about .85lbs underwater, and a dwarf wearing full plate and weighing 200lbs on land would likely weigh only about 170lbs while laying prone at the bottom of a Giant Crayfish pool. Multiply that by two dwarves, and you have about 340lbs.
Surely Eltrezar's weenie arms would still be ill-equipped to pull a rope bearing that sort of weight, but between himself and the four other party members standing around the pool's edge, all of whom have a 14 Strength, 70lbs apiece doesn't seem like anything we need to make an ability roll for...