Lake Vistytis (sometimes Lake of Vistytis; Russian: Vishtynetskoye ozero, Виштынецкое озеро; Lithuanian: Vištytis ežeras; informal sometimes European Baikal) is a lake on the border between Lithuania (Marijampole district) and Russia (Kaliningrad oblast). It is named after the small Lithuanian town of Vistytis on its northern shore.

Lake Vistytis covers an area of 335 km² most of which is in Russia. The frontier follows the waterline along the Lithuanian shore, so bathers on Lithuanian beaches actually enter Russian territorial waters.

It is situated within a picturesque landscape of forests and hills. The lake is a protected nature reserve and earns its "European Baikal" reputation because of the diversity of its unique flora and fauna.