The Usk River is the central waterway of the nation of Nidal in western Avistan. It has its source in Varisia and Nirmathas' Bloodsworn Vale in the southern Mindspin Mountains, and travels south past the Barrowmoor and through the Atteran Ranches. It is next joined out of the east by the Gjurn River that flows down from the city of Glimmerhold before reaching Usk Lake. The only outflow from Usk Lake is still named the Usk River, and it now travels west through the Uskwood and past the capital of Pangolais and the House of Lies before emptying into Nisroch Bay at the city of Nisroch. The Usk River bisects that city both geographically and economically: the rich live in the districts north of the Usk, while the poor huddle south of it.
The Usk River is one of the few partially navigable rivers that lead into the heart of the Mindspin Mountains. From the Bloodsworn Vale down into the lowlands of Nidal, the river cuts a deep ravine through the mountains.
A coven of green hags known as the River Maidens impose sinister demands on those who reach the Usk River's headwaters. The hags guard a series of tunnels that connect the river's headwaters to the Bloodsworn Vale. A large number of minions serve the hags.