The blue expanse of the Nyr Dyv is the largest known fresh-water lake upon Oerik. Midbay, where the waters of that lake gather to form the Selintan River, is one of its most placid regions.
The Nyr Dyv has three major inlets (the Artonsamay, Veng, and Velverdyva Rivers), and an outlet greater than the Selintan in the Nesser River. All of these are even more navigable than the Selintan, and thus the lake has become a major center of commerce in the known world.
Monsters of a variety of horrid types are known to dwell in the Nyr Dyv’s darkest reaches (its name means “Lake of Unknown Depths”). Fortunately, the shallow waters of the Midbay seem to prevent these creatures from intruding there.
Naval fleets from several bordering nations patrol the waters of the lake, protecting commerce against piracy or, more often, seeking and slaying the troublesome sea serpents wherever they can be found.
The Lake of Unknown Depths is said to have once held a number (sources vary between three and seven) of very magical islands called the Isles of Woe, which apparently sank beneath the waters over a thousand years ago. The Isles are reputed to have been the home of the wizard-priest Tzunk, who used the Codex of the Infinite Planes to rule an empire. Other sources claim that the archlich Vecna ruled his ancient domain from an island in this area.
Regardless of these rumors, the Nyr Dyv is a hub of marine traffic for all countries that abut it. Even the far reaches of the Flanaess trade here using the lakes great tributaries or the two large rivers that drain from it. The lake is also home to most of the Rhennee, and the bargefolk are said to know the Nyr Dyv very well. Piracy is rare on the lake, as the Furyondian marines have taken great pains to arrest independent buccaneers and chase away the predatory craft of Iuz. Strange sea monsters make regular appearances, and most warships have had at least one conflict with such a creature that sought to sink it or steal its crew.