Possible Clues:

• Szczecin's river
• Poem written on river, one in central Europe
• Duck on the German river
• It has banks in Germany and Poland
• That's perhaps a stinking flower of Germany
• Poem written on river, one flowing into Baltic
• River that, with the Neisse, forms the German-Polish border
• Flower that's yellow, outside Germany or in it
• European river’s unpleasant effluvium, so to speak
• River current taking out both banks?