Kotra (river)

{{About|a river|other uses|Kotra (disambiguation)}}

{{Infobox river

| name = Kotra

| image =Katros upė ties Pogarenda.JPG

| image_caption = Kotra River in Pogarenda (Belarus-Lithuania border)

| source1_location = 22 km southeast from Varėna

| mouth = Neman

| mouth_coordinates = {{coord|53|33|53|N|24|02|36|E|display=it|region:BY_type:river_source:kolossus-ruwiki}}

| progression = {{RNeman}}

| subdivision_type1 = Country

| subdivision_name1 = Belarus, Lithuania

| length_km = 109

| source1_elevation =

| mouth_elevation =

| discharge1_avg = {{convert|12.8|m3/s|cuft/s|abbr=on}}

| basin_size_km2 = 2010

| extra = {{Designation list

| embed = yes

| designation1 = Ramsar

| designation1_offname = Cepkeliai mire

| designation1_date = 20 August 1993

| designation1_number = 625{{Cite web|title=Cepkeliai mire |website=Ramsar Sites Information Service|url=https://rsis.ramsar.org/ris/625|accessdate=25 April 2018}}

| designation2 = Ramsar

| designation2_offname = Kotra

| designation2_date = 21 October 2002

| designation2_number = 1216{{Cite web|title=Kotra|website=Ramsar Sites Information Service|url=https://rsis.ramsar.org/ris/1216|accessdate=25 April 2018}}}}

}}

The Kotra ({{langx|be|Котра}}; {{langx|lt|Katra}}) is a {{convert|109|km|mi|adj=mid|-long}} river in Belarus and Lithuania. The river is an example of a rare phenomenon of river bifurcation.

At first, the Kotra and Ūla form one river, known as the Pelesa, which originates in Belarus and flows in a northwesterly direction. Just past the Belarus–Lithuania border, between the villages of {{ill|Paramėlis|lt|}} and Kazliškės, some {{convert|22|km}} 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. The bifurcation happened 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 {{convert|410|km2}} 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 {{convert|24|km}} and the remaining {{convert|85|km}} 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 {{convert|20|km2}} of open marshes overgrew with trees. The Kotra and its surrounding marshes form wetlands of international importance: Kotra Ramsar site and Cepkeliai Ramsar site{{Cite web|url=https://rsis.ramsar.org/ris/625|title=Cepkeliai mire | Ramsar Sites Information Service}} Varėna district municipality established a {{convert|1.085|km2|adj=on}} reservoir to protect the natural Kotra environment.