Calassa
From Grimhaven Wiki
An underwater location northeast of the island of Nargor with all types of Quara as well as Water Elementals and Massive Water Elementals. You can only get there from Captain Max's ship after renting a Helmet of the Deep from him for (5000gp) and putting it on your head.
Calassa is home to one of the missions from the Explorer Society Quest.
Creatures found on the island: Quara Constrictor, Quara Mantassin, Quara Hydromancer, Water Elemental, Massive Water Elemental, Quara Pincher, Quara Predator.