Lake Ladoga (Russian: Ладожское озеро, Finnish: Laatokka) is the largest lake in Europe, located in Karelia, since WWII in northwestern Russia near the border to Finland.

The area of the lake is 17,700 km² (approximately 6,800 square miles). The lake drains into the Gulf of Finland of the Baltic Sea via river Neva.

Ladoga has its own endemic Ringed Seal subspecies.

The most important tributaries are:

• River Svir from lake Onega
• River Vuoksi from lake Saimaa in Finland

Border between East and West

1617–1721 the border between Sweden and Russia was drawn through Lake Ladoga, like later 1812–1940 the border between Finland and Russia.

The 10th century Valamo Monastery was founded on the island of Valaam (Finnish: Valamo), the largest in Lake Ladoga, desolated 1611–1715, magnificently restored in the 18th century, and finally evacuated to Finland during the Winter War in 1940. In 1989 the monastic activities were started again.

During the siege of Leningrad, 1941–1944, lake Ladoga provided the only access to the besieged city. Supplies were transported into Leningrad with trucks on winter roads over the ice, the "Road of Life", and by boat in the summer.