(Belorussian Neman, German Memel) The principal Lithuanian river, 937 km long. Flows through Belorussia, Lithuania and along Lithuanian-Russian border. In the past (XIIIth - XVIIIth centuries) almost the entire Nemunas basin was accomodated in the territory of the Lithuanian state. The river flows from east to west and empties into Courish Lagoon.
The river starts in some swampy wood somewhere in Belorussia and flows through marshy, underpopulated valley with few roads and bridges. After receiving the waters from Katra above Gardinas, Nemunas turns north and flows to Kaunas, where it meets Neris, the second biggest Lithuanian river. Nemunas and Neris are often referred in Lithuanian folklore as `the father and the mother of rivers'. In 1959 the river was dammed above Kaunas for a hydro-electric power plant. This has created a so called Kaunas Sea. Below Kaunas, Nemunas flows through some flood plains which are usually flooded in springtime. The Nemunas flows into Courish Lagoon after entering its delta which streches for 5-6 kilometres.
The many ruined castles and fortresses along the Nemunas river speak of its colorful and dramatic past. From the ends of XIVth century onwards the lower Nemunas was the scene of warfare between Lithuanians and the Teutonic Order. The latter, having conquered Prussia, used the river to penetrate deeper into Lithuania. I should remind you that at the time Lithuanians were the last remaining pagans in Europe, and Teutonic Order wa trying to christen them. the fortresses along Nemunas were built either as defense posts or bases for attack, they were frequently destroyed rebuilt by one side or another. After the defeat of Teutonic Order in 1410 the fighting stopped and castles only served only residential purpose for the nobility or fell into ruin.
The first written records about navigation date from mid-XIIIth century. Boats transported grain and other farm products downstream, returning with salt and other goods being towed upstream by the crew. Later, the river was primarily used for floating logs to Klaipeda
I could add that nowadays the river is quite polluted, but is still suitable for fishing and some people even swim in it (not me though)