Núrnen was located in the southeast of Mordor. It was fed by rivers flowing down from the outcroppings of the Ephel Dúath and Ered Lithui that separated the volcanic plateau of Gorgoroth from the fertile volcanic plains of Núrn, and its waters were described by Tolkien as "the dark, sad waters of Lake Núrnen". Its waters are often claimed to have been saltwater, but this is not supported in any of Tolkien's writings. Its waters were likely used for irrigation purposes to water the fields of Nurn.