Fed by three rivers, Lake Mulsantir is a turbulent muddle of silty runoff, murky depths, and strange currents that can overturn craft or suddenly sweep a person away. Its waters flow north into Lake Ashane through a broad passage called the River Mulsantir. Rashemen patrols the lake with magically animated witchboats, piloted by hathrans. The Mulsantir is less cold than the Ashane and contains more varieties of fish, so many fisher folk work here despite the dangers.
Thay used to battle Rashemen for control of the lake, but Thay has less lumber than Rashemen, and the witchboats are far more maneuverable than any vessels of the Red Wizards. Thay eventually stopped aggressive action on the lake, preferring to invade across the River Mulsantir to the north. The Red Wizards dumped magically crossbred monsters into the lake in hopes of upsetting the witchboats, but the currents and cold made the monsters hug the southern shores and prey on Thayan vessels and settlements, so they abandoned that practice. Boats disappear more often here than even the difficult waters would explain, so it is likely that some of these creatures remain and occasionally surface to grab a snack before retreating to the comforting darkness.