Eight large rivers flow down from the Caucasus ranges into the central Kura-Aras lowlands, alluvial flatlands and low delta areas along the seacoast designated by the Azerbaijani name for the Mtkvari River and its main tributary, the Aras. The Mtkvari, the longest river in the Caucasus region, forms the delta and drains into the Caspian a short distance downstream from the confluence with the Aras. The Mingechaur Reservoir, with an area of 605 square kilometers that makes it the largest body of water in Azerbaijan, was formed by damming the Kura in western Azerbaijan. The waters of the reservoir provide hydroelectric power and irrigation of the KuraAras plain. Most of the country's rivers are not navigable.