The Kotra ( be, Котра; lt, Katra) is a river in

Belarus Belarus,, , ; alternatively and formerly known as Byelorussia (from Russian ). officially the Republic of Belarus,; rus, Республика Беларусь, Respublika Belarus. is a landlocked country in Eastern Europe. It is bordered by R ...

and

Lithuania Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...

. The river is an example of a rare phenomenon of

river bifurcation River bifurcation (from la, furca, fork) occurs when a river flowing in a single stream separates into two or more separate streams (called distributaries) which then continue downstream. Some rivers form complex networks of distributaries, typi ...

. At first, the Kotra and

Ūla The Ūla ( be, Ула) is a river in Dzūkija National Park in southern Lithuania and northern Belarus. Its total length is 84 km. The Ūla flows into the Merkys The Merkys ( be, Мяркіс ''Miarkis'') is a river in southern Lithuania ...

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 and Kazliškės, some southeast of

Varėna Varėna (; pl, Orany; yi, אוראַן ''Oran'') is a city in Dzūkija, Lithuania. History The town was founded in 1862 near the Warsaw – Saint Petersburg Railway, south of Sena Varėna (Old Varėna). At that time it was a small settleme ...

, it branches out into two independent rivers: the Kotra, a tributary of the

Neman The Neman, Nioman, Nemunas or MemelTo bankside nations of the present: Lithuanian: be, Нёман, , ; russian: Неман, ''Neman''; past: ger, Memel (where touching Prussia only, otherwise Nieman); lv, Nemuna; et, Neemen; pl, Niemen; ...

, and the Ūla, a tributary of the

Merkys The Merkys ( be, Мяркіс ''Miarkis'') is a river in southern Lithuania and northern Belarus. It flows for through Belarus, along the Belarusian–Lithuanian border, and through Lithuania before joining the Nemunas near Merkinė. Merkys is ...

. This situation arose in the second half of the 19th century when the Ūla, due to its channel erosion, crossed the

water divide A drainage divide, water divide, ridgeline, watershed, water parting or height of land is elevated terrain that separates neighboring drainage basins. On rugged land, the divide lies along topographical ridges, and may be in the form of a singl ...

between its own and the Kotra's

drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, t ...

s. As a result, the Ūla 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 Belarus–Lithuania border for and the remaining through Belarus. It then flows along the southern border of

Čepkeliai Marsh The Čepkeliai Marsh ( lt, Čepkelių raistas) is the largest bog (a mire) in Lithuania. Located in Varėna District Municipality, south of Marcinkonys village and north of Kotra River, which flows along the Belarus–Lithuania border in this a ...

, the area protected as a

nature reserve A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, or features of geological or ...

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

Varėna district municipality Varėna (; pl, Orany; yi, אוראַן ''Oran'') is a city in Dzūkija, Lithuania. History The town was founded in 1862 near the Warsaw – Saint Petersburg Railway, south of Sena Varėna (Old Varėna). At that time it was a small settleme ...

established a reservoir to protect the natural Kotra environment.

References

* * *
Cepkeliai
. ''Long Term Ecological Research (LTER) Network in Lithuania''. Institute of Ecology of Vilnius University. Accessed 9 October 2006.

External links

Information Sheet on Ramsar Wetlands (PDF)Environmental Changes in the Ūla and Katra Upper Reaches During the Last 14,000 Years (PDF)
{{Tributaries of the Neman Rivers of Grodno Region Rivers of Lithuania International rivers of Europe Belarus–Lithuania border Ramsar sites in Belarus Rivers of Belarus