The Vardar is the longest river in Macedonia, flowing 388 km from its source near Gostivar to its mouth emptying into the Aegean Sea west of Thessaloniki in Greece. It passes through Skopje and Veles before crossing into Greece. The Vardar basin drains over two-thirds of Macedonia and comprises fertile lands along the river valley. The Vardaris wind blows powerfully down the river valley, bringing cold conditions to Thessaloniki. The river's name derives from the Thracian word for "black water."