The Edgewater River was an enormous river running from the Spring of Riverrise in the east to the furthest tip of the Edge in the west, which it cascaded over in a spectacular waterfall. On its journey it passed through the Nightwoods, the Deepwoods, the Twilight Woods, the Mire, the City of Undertown, and finally the Stone Gardens.
Near its source in Riverrise the river's waters had magical and rejuvenating qualities, but as it ran further and further away it became increasingly polluted. By the time it reached the Stone Gardens, it was toxic and foul, predominantly from the waste expelled by Undertown's many sewers and factories.
Every five or six thousand years, the Riverrise Spring would run dry and the Mother Storm would return to renew it. This formed a critical plot point in Midnight Over Sanctaphrax, when the construction of Sanctaphrax blocked the Mother Storm's path.