The Nedonas (Greek: Νέδωνας, older form: Nedon) is a river Messenia, Peloponnese, Greece. It is approximately 30 km long.
The river rises on the western slope of the Taygetus mountains, at around 1,100 m elevation, near the village Artemisia. It flows in southwestern direction, through a steep and narrow gorge. It is fed by several small tributaries, including the Nedousa. It flows through the city centre of Kalamata, where it empties into the Messenian Gulf. The Greek National Road 82 (Pylos - Kalamata - Sparta) runs along the river for a part of its length.