For some reason serveral large objects are missing on Wikimedia maps, e.g.:

• Lake Ladoga (https://www.openstreetmap.org/relation/1754729),
• Lake Onega (https://www.openstreetmap.org/relation/1308279),
• Lake Baikal (https://www.openstreetmap.org/relation/555716),
• Lake Balkhash (https://www.openstreetmap.org/relation/3367363) — east part etc.

Take a look at the map on https://en.wikivoyage.org/wiki/Saint_Petersburg_(district)

Ladoga Lake is not visible on the Wikimedia layer of the map on the left, but the lake is present on the Mapnik layer of the map on the right.