The Alva'atan ("Mother River") is the largest river system of Ishkrond, and the largest known river on Nuerth. It extends some 6,000 miles from its headwaters in the mountains of the Hidden Kingdom. From the mountains, the river flows east through the Great Jungle Basin, a vast rainforest inhabited by jaguars, elephants, tapirs, anacondas, river dolphins, and other fauna. The river eventually turns south and flows through woodlands, savannah, and chapparal before emptying into the Sea of Snakes. Agriculture in Ishmodia and other lands of the lower Alva'atan depends on the Alva'atan for water, which is distributed through a complex network of irrigation canals and aquaducts. The annual floods of the river cover huge expanses of low lying land, renewing the land and providing essential nutrients.
The wide river is navigable by sea-going ships for much of its length, though at several sites (including just below Gyr), cataracts must be bypassed by canals.