Lake Generosity

Description
Lake Generosity once surrounded the Shrine of Sacrifice in north-eastern Britannia, a forested and generally fertile area. It was the third-largest lake of Britannia. However, ironically fitting for the virtue of Sacrifice, a climate shift caused the area to fall dry, turning it into a desert. In the course of this process, Lake Generosity evaporated, leaving the shrine alone in the inhospitable desert of the Dry Lands.

Interestingly enough, by Ultima VII, a small climate shift had caused a part of Lake Generosity (although not much) to re-fill, again surrounding the shrine.

Lore
Britannia's third large lake, the one-time picturesque Lake Generosity, was a casualty of the great drought of the northeast and is now simply a bed of dry sand.

-from "The Book of Lore", Ultima V