Ladoga Lake

From Openwaterpedia

Lake Ladoga is a freshwater lake located in the Republic of Karelia and Leningrad Oblast in northwestern Russia in the vicinity of Saint Petersburg. It is the largest lake entirely in Europe and the 14th largest freshwater lake by area in the world.

Open Water Swimming

It is site of the Valaam Swimming Marathon, a 20 km open water swim from the island of Putsaari to the island of Valaam in Ladoga Lake.