In Barren Coast: (no data)
In the Buried Sea: (no data)
In Sanctum Somnium: Part of the third raid event in Sanctum Somnium, "Under the Sea" (see this quest entry for event and loot information).
In Sarith (non-instanced): Sees invisible; hits for a max ~11,000; rootable; does not summon.
In Sarith (instanced): Appears in the water after the High Priest is engaged.