Fihrgrell is an ocean of the Abyss world Kurun'Ush.
In the Demon Spawn War, a rift was opened at the head of Bal-Kriav's Moredhel Valley. This created a link between this valley and an ocean of another world. At of the Moredhel-Fihrgrell Rift (9266 GE), seawater flooded the valley. It created lake Moharr, then continued west, draining into the Ratanur Trap. It was named thus because of a null mine used to create a counter rift, one that fittingly came to be known as the Fihrgrell Drain (9274 GE).
In 9457 GE, Thyrm, serving under the Quarat'un Covenant, stoppered the Moredhel-Fihrgrell Rift with The Frozen Titan, the area around it became the unnatural glacier Fihrgrell Cap. With a dam in place, the flow from one side of the rift to another was reduced to the natural melting of the glacier around.
Remnants of this ocean are still on the world Bal-Kriav, with the lower depths of Lake Dynaer the most concentrated.