From WoWWiki

The Nazferiti River is a very long river, the longest in the Eastern Kingdoms, and competing with the Southfury River for the longest river in Azeroth.

It rises in Deadwind Pass and can be seen tumbling down a waterfall in southern Redridge Mountains. It then flows west, bordering Duskwood and the Elwynn Forest. A tributary flowing from the mountains northwest of Stormwind City tumbles into the river and there the river sharply turns and heads south, marking the borderline of Westfall with the Elwynn Forest, and further south, Duskwood. The river flows into the jungles of Stranglethorn Vale and tumbles into Lake Nazferiti. Finally, the Nazferiti River pours into the Great Sea south of the Grom'Gol Base Camp.