The Kotra (; ) is a river in Belarus and Lithuania. The river is an example of a rare phenomenon of river bifurcation.
At first, the Kotra and à ªla form one river, known as the Pelesa, which originates in Belarus and flows in a northwesterly direction. Just past the BelarusâÂÂLithuania border, between the villages of and Kazlià ¡kÃÂs, some southeast of VarÃÂna, it branches out into two independent rivers: the Kotra, a tributary of the Neman, and the à ªla, a tributary of the Merkys. The bifurcation happened in the second half of the 19th century when the à ªla, due to its channel erosion, crossed the water divide between its own and the Kotra's drainage basins. As a result, the à ªla enlarged its basin by some and the Kotra lost two of its tributaries. These processes also caused a decrease in groundwater levels and the almost total disappearance of several lakes in the area.
The Kotra flows along the BelarusâÂÂLithuania border for and the remaining through Belarus. It then flows along the southern border of ÃÂepkeliai Marsh, the area protected as a nature reserve With the changes in drainage basins and groundwater levels, some of open marshes overgrew with trees. The Kotra and its surrounding marshes form wetlands of international importance: Kotra Ramsar site and Cepkeliai Ramsar site VarÃÂna district municipality established a reservoir to protect the natural Kotra environment.
The name Katra/Kotra is very unclear. Aleksandras Vanagas reconstructed a very dubious Proto-Indo-European root *kataro- ('a trench, rivulet, stream', as for Italian river Catarona or Liburnian river ÃÂñÃÂñÃÂòìÃÂ÷ÃÂ) from which originated the name of the river. Simas Karalià «nas suggested a Slavic borrowing in Lithuanian katãryti/katãlyti (from ) 'to beat, to whip' as a possible source of the name. Edward Bogusà Âawski presented Kotra as a Finno-Ugric name (without further elaborating it; Rimvydas Kunskas suggested 'to flood (kaataa) a backgarden (tarha)'). à  arà «nas à  imkus suggests the name may come from a pronoun , , 'which [of both]' (fem.) as a reference to a very tangled upper course of this river.