Related Clues:

• River subject of a 1990 German/Polish treaty
• River that empties into the Baltic Sea
• River current taking out both banks?
• European river’s unpleasant effluvium, so to speak
• A German river flowing through a city called Frankfurt
• Flower that's yellow, outside Germany or in it
• River that, with the Neisse, forms the German-Polish border
• River in central Europe that forms part of the boundary between Poland and Germany
• River finished with a hundred-fold increase in content
• *More bizarre
• It forms part of Germany’s eastern border
• It flows into the Szczecin Lagoon
• German river leading, in essence, to Cologne, do we hear?
• Duck beginning to dabble with hesitation in river
• Germany-Poland border river