Lake Peipus, (Estonian: Peipsi järv, Pihkva järv; Russian: Чудско-Псковское озеро (Chudsko-Pskovskoe ozero), German: Peipussee) is the biggest transboundary lake in Europe on the border between Estonia (part of European Union) and Russia.
The lake is the fifth largest in Europe after Lake Ladoga and Lake Onega in Russia north of St. Petersburg, Lake Vänern in Sweden, and Lake Saimaa in Finland.
Lake Peipus is a remnant of a bigger body of water which existed in this area during an Ice Age. It covers 3,555 km2, and has an average depth of 7.1 m, the deepest point being 15 m. The lake has several islands and consists of 3 parts:
The lake is used for fishing and recreation, but suffered from some environmental degradation from Soviet era agriculture. Some 30 rivers and streams discharge into Lake Peipus. The largest rivers are Emajõgi and Velikaya River. The lake is drained by the Narva River.
In 1242, the lake was the site of the Battle on the Ice (Estonian: Jäälahing) between the Teutonic Knights and Novgorodians under Alexander Nevsky.