The Psou (; ; ; ) is a river in the West Caucasus, bordering the Gagra Range of Abkhazia to the east. It flows along the southern slopes of the Greater Caucasus Mountain Range and forms a part of the border between Abkhazia and Russia. Its source in the Aigra Mountain, and it flows into the Black Sea. The Psou is long, and the drainage basin is approximately . Between the mouth of the river and the mouth of the Mzymta is a sandy depositional foreland, which is approximately in length and wide.