Possible Clues:

• River's middle avoided by stranger
• Part of the Poland-Germany border
• River forming part of German-Polish border
• Nothing is dumped beside the German waterway
• River that flows to the Black Sea
• River of Poland
• Sounds like what you get from the Liffey, though not in Dublin
• River duck with a red back
• Streaming stink sound
• Smell reported in European river