Kotra River

Kotra River (Lithuanian: Katra) is a 109-kilometre (68 mi) long river in Belarus and Lithuania. The river is known due to a rare phenomenon of river bifurcation.

At first Kotra and Ūla Rivers form one river, known as Pelesa River. Pelesa originates in Belarus and flows in northwestern direction. Just pass the Belarus–Lithuania border, between Paramėliai and Kazliškės villages situated some 22 kilometres (14 mi) southeast of Varėna, it branches out into two independent rivers: Kotra, tributary to the Neman River, and Ūla, tributary to the Merkys. Such situation developed in the second half of the 19th century when Ūla due to its channel erosion crossed the water divide between its own and Kotra's drainage basins. As a result Ūla enlarged its basin by some 410 square kilometres (160 sq mi) and Kotra lost two of its tributaries. Also, these processes have caused a decrease of the groundwater levels and almost total disappearance of several large lakes located in the site.

Kotra flows along the Belarus–Lithuania border for 24 kilometres (15 mi) and the remaining 85 kilometres (53 mi) through Belarus. Kotra flows along the southern border of Čepkeliai Marsh, an area protected as nature reserve. With the changes in drainage basins and groundwater levels some 20 square kilometres (7.7 sq mi) of open marshes overgrew with trees. Kotra and surrounding marshes form wetlands of international importance. Varėna district municipality established a 1.085 square kilometres (0.419 sq mi) reservoir to protect natural Kotra environment.