In historical terms , the river fell within the area of the medieval Monastic state of the Teutonic Knights established in the 13th century . The adjacent territory became later known as East Prussia , and then an easternmost province of Germany until 1945 when , in accordance with border changes promulgated at the Potsdam Conference , it was split between Poland and the Soviet Union
Potsdam Conference
Potsdam Conference
Łyna (river)