Wisłok River [Ukrainian: Вислок (Vyslok) or Вислік (Vyslik)]. (Map: Wisłok River.) A left-bank tributary of the Sian River that flows for 228 km through Slovakia and Poland and drains a basin area of 3,540 sq km. In the Princely era most of the river and its basin area formed part of the realms of Kyivan Rus’ or the Principality of Galicia-Volhynia. Ukrainians inhabited the upper part of the river (in addition to forming a few pockets of Ukrainian settlement between the Wisłok River and the Sian River) until the late 1940s, when they were forcibly resettled during Operation Wisła.
[This article originally appeared in the Encyclopedia of Ukraine, vol. 5 (1993).]