Nemunas (Neman) is a major Eastern European river rising in Belarus and flowing through Lithuania before draining into the Curonian Lagoon and then into the Baltic Sea at Klaipėda. It is the northern border between Lithuania and Russia's Kaliningrad Oblast in its lower reaches. It also very briefly forms part of the border between Lithuania and Belarus. The 14th largest river in Europe, the largest in Lithuania and the third largest in Belarus, it is navigable for most of its 900-kilometer length.
The Neman River basin was formed during the Quaternary period, and is located roughly along the edge of the last glacial sheet, dating from about 25,000 – 22,000 years BP (before present). Its depth varies from one meter in its upper courses to five meters in the lower basin.
• The total length of the Neman is 937  kilometers (582  miles). It is the 14th longest river in Europe and the 4th longest in the Baltic Sea basin. Over its entire length, 459 km (285  miles) flows in Belarus and 359 km (223 mi) in Lithuania. A 116 - kilometer stretch is the border between Lithuania and Russia's Kaliningrad oblast.
• Its greatest depth is five meters (16.4 ft), and at its widest it extends about 500 meters (1640 feet).
• The Neman is a slow river; it flows at about one to two meters/second.
• During floods, water discharge can increase up to 11-fold, to more than 6,800 m³/s. Severe floods occur on the lower reaches of the river about every 12 – 15 years, which sometimes wash out bridges.[2]
• The Neman is an old river, dating back to the last glacial period. Its valley is now up to 60 meters deep and five kilometers broad.
• The Neman has about 105 first-class tributaries, the largest being the rivers Neris (Viliya) (510 km/317 miles), the Shchara (325 km/202 miles), and the Šešupė (298 km/185 miles). Fifteen of the tributaries are longer than 100 km (62 mi).
• In the Neman basin there are tributaries extending to the 11th order.
• The Neman basin in Lithuania drains more than 20,000 rivers and rivulets and covers 72% of Lithuania's territory.
• The total area of the Neman basin is 97,863 square kilometers; the Lithuanian portion of this basin is 46,695 square kilometers.

The largest cities on the Neman are Hrodna in Belarus, Alytus and Kaunas in Lithuania, and Sovetsk in the Kaliningrad Oblast of Russia. The river basin has a population of 5.4 million inhabitants. Industrial activities in the Belarusian section include metal processing, chemical industries, pulp and paper production, and manufacturing of building materials, as well as food-processing plants. In Lithuania the city of Kaunas, with about 400,000 inhabitants, is the country's principal user of the river; the local industries that impact the river are hydropower generation, machinery, chemical, wood processing and paper production, furniture production, textile and food-processing. In Kaliningrad, industrial centres near the river include Sovetsk and Neman, which have large pulp and paper production facilities.

Above Kaunas a dam was built in 1959 to serve the Kaunas Hydroelectric Power Plant. The resulting Kaunas Reservoir (Lithuanian: Kauno marios) is the largest such lake in Lithuania. It occupies 63.5 km2 (24.5 sq mi); its length is 93 km (58 mi); its greatest depth is 22 m (72 feet). The reservoir is a popular destination for Lithuanian yachting.