The Unified Deep Water System of European Russia (Russian: Единая глубоководная система Европейской части Российской Федерации, romanized: Yedinaya glubokovodnaya sistema Yevropeyskoy chasti Rossiyskoy Federatsii) or UDWS (Russian: ЕГС) is a system of inland waterways in Russia linking the White Sea, the Baltic Sea, the Volga River, Moscow, the Caspian Sea and—via the Sea of Azov—the Black Sea. In 2010, UDWS carried 70 million tons of cargo and 12 million passengers, making up two-thirds of overall inland waterway traffic volume in Russia. There are 60 common-use ports and quays in the UDWS, including three international ports (two in Moscow and one in Dmitrov, Moscow Oblast), so Moscow is sometimes called "the port of the five seas".
The depth is mostly guaranteed at only 4 metres (13 ft) and some sections are even shallower, such as Gorodets–Nizhny Novgorod at 2.5 metres (8.2 ft) and Kochetovsky Bagayevskaya at 3.2 metres (10 ft). There are plans to increase depth of these sections to 4 m.
