Bóbr  Bóbr (, , ) is a river which carries water through the north of the Czech Republic and the southwest of Poland, a left tributary of the Oder. The Bóbr has a length of (3 in Czech Republic, 276 in Poland, 10th longest Polish river) and a basin area of (44 in Czech Republic and 5,830 in Poland). It originates on a slope of the Rýchory mountains in the southeast of the Krkonoše range. The source is located near the small Bobr village of the Žacléř municipality in the Czech Hradec Králové Region. Parallel to the Lusatian Neisse tributary of the Oder in the west, it flows northwards from the Bohemian region into adjacent Silesia. Shortly after the river crosses the border to Polish Niedamirów and runs northwestwards through the Jelenia Góra valley of the Western Sudetes to the dam of Pilchowice and downhill into the plains of Lower Silesia, passing the towns of Jelenia Góra, Bolesławiec, Szprotawa, and Żagań, where the parallel Kwisa river joins it. The river finally flows into the Oder near the town of Krosno. Non-navigable for its entire length, it is a popular destination for canoeing. Since the Middle Ages the lower Bóbr river north of Żagań and the Kwisa confluence marked the border between the historic regions of Silesia in the east and Lower Lusatia to the west. After in 937 King Otto I of Germany had established the Saxon Eastern March on the lands settled by Polabian Slavs, Margrave Gero until 963 subdued the Lusatian lands up to the border with Poland ("Civitas Schinesghe"). Upon Gero's death in 965, the river was the designated eastern border of the newly created March of Lusatia in the Holy Roman Empire. The Polish territorial sovereignty was acknowledged to Duke Bolesław I Chrobry by Emperor Otto III at the Congress of Gniezno in 1000. Nevertheless, Bolesław laid claims to the lands west of the Bóbr, which he temporarily acquired by the 1018 Treaty of Bautzen. After Emperor Conrad II had reconquered the territory until 1031, the "status quo" was restored.