Kotra (river)

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

Map of Katra

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

The Kotra flows along the Belarus–Lithuania border for 24 kilometres (15 mi) and the remaining 85 kilometres (53 mi) through Belarus. It then flows along the southern border of Čepkeliai Marsh, the area protected as a 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. The Kotra and its surrounding marshes form wetlands of international importance: Kotra Ramsar site and Cepkeliai Ramsar site Varėna district municipality established a 1.085-square-kilometre (0.419 sq mi) reservoir to protect the natural Kotra environment.