The Azure Leviathan

Along the shores of Iqari and in numerous island settlements across the southern hemisphere, legends are told about how The Great Azure Ocean is itself alive. Many believe these stories to be nothing more than myths told in village gatherings meant to scare children into being cautious in the water, or otherwise perpetuated by older kids around campfires to give the younger ones nightmares.
The stories describe how the surface of the water breaks ahead of ships and forms into an inconceivably large serpentine form, only to then crash down mouth open onto the vessel and swallow it whole, dragging the poor souls aboard down to the ocean's depths. Others report of a similarly gargantuan waterborne serpent emerging and washing over entire seaside villages, leaving nothing but broken soaking timbers in its wake. In the southernmost communities, these myths vary in that their version of the liquid serpent is adorned with spines and fangs of ice, and though it seems to move more slowly the destruction it yields is certainly comparable.
But while these legends often sound exaggerated, they are all too tangible. Ships traversing the Azure Ocean mysteriously vanish without a trace, or wash up hundreds of miles away from where they should have been. Entire coastal and island settlements have been found left in ruins as though they were crushed by an impossibly powerful tsunami. Regardless of what people think it may be, surely something ancient and destructive wanders the world's largest ocean...