The Merkys (Belarusian: Мяркіс, romanized: Miarkis) is a river in southern Lithuania and northern Belarus.

The Merkys is mostly fed by underground streams and therefore is cooler during summers and has smaller fluctuations in water level than other rivers in Lithuania.

[1] At the end of the 19th century the drainage basin of the Merkys grew by some 410 km2 (160 sq mi) as its tributary Ūla overtook some of the Kotra's watershed area.

[1] The Merkys is a popular destination among water tourism enthusiasts as part of it belongs to the Dzūkija National Park and it flows into the Neman near the historical site of Merkinė.

[1] The name of the river, Merkys, originate from merkti, an appellative word in the Lithuanian language meaning to soak.