A vast salt swamp stretches along the Sword Coast shore over 100 miles, reaching a width of 30 miles at its greatest extent. It's a desolate, insect-ridden place seldom visited by civilized races and home to a variety of fell creatures. The Mere has grown in recent memory, swallowing several farms and holdings along the road, and is now avoided by all but crazed adventurers equipped with water-breathing magic and looking for battle practice.
Several rich castles and manor houses stand flooded in the Mere, with only spires and battlements showing above the dark waters. Sunken riches and powerful magic guarded by evil creatures await those mighty enough to take it. Khelben Arunsun advises adventurers that some of these flooded places (Castle Naerytar, Holk House, Mornhaven Towers, and Wolfhill House) have their own wards. These allow certain spells to be cast at increased strength, and other spells are negated. If these effects are still standing after the Spell Plague they are to be discovered by trial, for all relevant records are lost.
The Mere gained its name when thousands of men were slain by orc hordes striking south from present-day Triboar and east across the Stone Bridge and Ironford. The orcs pursued the men westward between the coastal peaks and slaughtered the human army as it was forced back into the icy waves.
Before it was swallowed by the ever-encroaching Mire, travelers on the High Road to the east often traveled for three days and nights without stopping to avoid camping near the waters. Will-o'-wisps bobbing over the water are common night sights on this stretch of road. Legends speak of floating islands, eerie pools of magical origin, lizard men commanded by liches, a penanggalan of monstrous size, and other fantastic creatures often used to scare children and entice adventurers. More recent tales come from a brave few that ventured into the dark waters of the swamp that mention dark tentacles of gargantuan proportions, yuan-ti slavers, temples to inhuman gods, giant leeches with bullywug riders, and a will-o'-wisp of monstrous size that pulsed with black energy.
One madman's ravings about a black wyrm have gone mostly ignored, save by his host, Blackrabbas Khuulthund, the Waterdhavian sage who now acts as the man's guardian. Blackrabbas believes this blackened wyrm that charmed the plants and darkened the air before him, could be the long-lost black dragon Chardansearavitriol. Yet other scholars believe Chardansearavitriol was killed in a battle far from the Mire and his territory taken by a younger black. Few folk are moved to investigate the dark, scum-coated waters of the Mere to learn the truth for themselves.
Self-styled bandit lords, such as Amalkyn the Black and the wizard Helduth Flamespell, have recently established holds in the hills. Dopplegangers dwell in some of the ruined villages and hamlets, taking the shapes of humans to lure weary caravans and traveling bands to their doom.