Deep-sea trench

In the modern age of Dominaria, the continental plate under the former Terisian island of Argoth is completely shattered. Because of this, there's a north-south deep-sea trench that runs almost all the way from Terisiare to Sarpadia in the south. Because of the Homarids living within the trench, it forms a nasty north-south divide in the Dominarian waters that's probably a real challenge for merfolk to pass through safely.