A largely unexplored location, the Undullain Ocean has remained mostly unexplored until fairly recent years. The waters are extremely difficult to navigate, even before the Blight, the open expanses having extremely dangerous currents and unexpected obstacles in the form of difficult to see peaks of seamounts that will tear apart ships quickly. The waters, just like the Ephemeral Sea, are toxic to a point, but a great deal of the toxicity is dispersed by the time the waters reach the Islands of Sanctuary and Apparatus.
Mostly submerged, undersea mountain ranges, rip currents, freak storms, and even floating islands have been documented prior to the modern age, and these things seem to have only gotten worse over the years since the Blight began to alter the face of Cairne. The most notable areas are the Islands of Sanctuary, and the Island of Apparatus.
Life beneath the waves has been drastically altered by the presence of the Void energies, but the waters furthest from the channels that carry water out from the Ephemeral Sea seem to have been able to sustain a great deal of the original fauna from pre-Blight times with only minimal mutations. While the majority of these creatures still remain altered, there are less drastic changes noted.