Lake Vištytis
View from Russian side to the Lithuanian shore
Lake Vištytis
Coordinates	54°26′N 22°44′E / 54.433°N 22.733°E / 54.433; 22.733
Primary outflows	Pissa
Basin countries	Lithuania, Russia
Max. length	8 km (5.0 mi)[1]
Max. width	4.2 km (2.6 mi)[1]
Surface area	17.83 km2 (6.88 sq mi)[2]
Average depth	15.5 m (51 ft)[1]
Max. depth	54 m (177 ft)[1]
Water volume	.258 km3 (0.062 cu mi)[1]
Surface elevation	172.4 m (566 ft)[1]
Settlements	Vištytis

Lake Vištytis (Lithuanian: Vištyčio ežeras, German: Wystiter See, Russian: Виштынецкое озеро) is a lake on the border between Lithuania (Vilkaviškis district) and Russia (Kaliningrad Oblast), near the tripoint with Poland.

The small Lithuanian town of Vištytis on the northern shore was named after the lake. In the west, the extended Romincka Forest stretches along the Russian-Polish border. On the Lithuanian side, the lake and its environs are part of a protected area named Vištytis Regional Park. The lake has 15 inflows, but only one river, the Pissa, tributary to Pregolya, flows from this lake.^[3]

Lake Vištytis covers an area of 17.83 km² (6.88 sq mi), of which 5.44 km² (2.10 sq mi) belongs to Lithuania.^[2] This is a marked increase over 0.4 km² (0.15 sq mi) that belonged to Lithuania before ratification of a Russian–Lithuanian border treaty in 2003.^[4] On occasion, high winds or broken equipment can force tourist boats to the opposite western shore.^[5][6] Even if unintentional, such incidents constitute illegal border crossings and can lead to sanctions from the border guards.^[5] Before the 2003 treaty, the border ran along the waterline of the beaches on the Lithuanian side, so anyone paddling in the water was technically crossing into Russia. Sometimes the lake is used for smuggling goods, usually cigarettes, across the border.^[7]

Prior to World War II the lake formed part of the border between the German province of East Prussia and Lithuania.