does it have river border?
Yes - the Elbe, the Werra and the Saale rivers
Inner German border
The border also ran along part of the length of three major rivers of central Germany: the Elbe between Lauenburg and Schnackenburg (around ), the Werra and the Saale. 
what is inner german border? It was a border between the German Democratic Republic (East Germany) and the Federal Republic of Germany (West Germany) from 1949 to 1990. was any escape method used here? Yes - by foot, hot-air balloon, swimming across the Baltic Sea
wiki:17881532
Inner German border [SEP] River borders
The border also ran along part of the length of three major rivers of central Germany: the Elbe between Lauenburg and Schnackenburg (around ), the Werra and the Saale. The river borders were especially problematic; although the Western Allies and West Germany held that the demarcation line ran along the eastern bank, the East Germans and Soviets insisted that it was located in the middle of the river (the Thalweg principle). In practice, the waterways were shared equally but the navigation channels often strayed across the line. This led to tense confrontations as East or West German vessels sought to assert their right to free passage on the waterways.