Deep Blue Ocean

There is a saying that there is nothing more dangerous than the ocean (except maybe for a scorn woman with the access to magic powers). And the ocean surrounding the islands of Avalonia is mighty dangerous indeed (so try your best to not upset the locals if you do not want to end up with a curse or two for the next ten generations). Sometimes, one could almost believe that there is someone on purpose trying to make the waters as dangerous and unstable as possible to keep everyone constrained to the island and not let them venture out under any circumstances. 
Deep Blue Ocean is not a safe place to be even if you are a fish or any other water-thriving animal. It has its fair share of predators, natural and supernatural, unexplored depths full of traps lurking on the bottom of it and many untamed disasters that can meet with you if you try to sail it. 
Not many people are actually skilled or foolish enough to attempt to travel far by boat, but occassional giant vessel with massive sails of exotic colours do make it all the way to the shores of the islands. It is rare for the travellers to arrive completely unscathed, so the coast towns and ports are full of stories about the beasts lurking below the waves, luring sailors into the depths with their songs and sparkly pearly jewels or with promises of immense glory. 
Those foolish dreamers who believe those tales and try to go diving for riches are in for a rude not-awakening-as-they-tend-to-most-surely-drown-and-sink-all-the-way-to-the-bottom-themselves-adding-onto-the-skeleton-army-growing-in-there-oops-spoilers. Only select few faeries and specially trained individuals are able to hold their breaths for more than a couple of minutes and magic regarding human breathing has always been limited as well. But who knows, maybe that will change in the near future and the Deep Blue Ocean will finally reveal all of its secrets.