(Kuršių ļlanka, or Kuršių Marios, from an ancient Baltic tribe, the Curonians, or Kuršiai), a lagoon on the southeastern shore of the Baltic Sea, in the Lithuanian SSR and Kaliningrad Oblast, RSFSR. It is cut off from the sea by the Courland Spit and is connected with it by the narrow Klaipeda Strait (390 m wide). The lagoon has an area of 1,610 sq km, a length of 93 km, an average width of 17.3 km, an average depth of 3.7 m, and a maximum depth of 7 m. The Nemunas River empties into the Courland Lagoon. The lagoon freezes over in winter and remains solidly frozen for 80 days; in summer its surface water warms up to 25°C.
The lagoon is an important fishing area. The major commercial fishes are carps, vimba, pike perch, bream, smelt, and eel. A biological station for the observation and banding of birds is located on the eastern shore. The cities of Klaipeda and Neringa are situated on the coast of the Courland Lagoon.