Possible Clues:

• River flowing along the Polish/German border
• Germany's ___-Spree Canal
• Party of engineers going up European river?
• What a stinking-sounding flower, perhaps
• This flower hasn't got a scent, it's got, a stink, by the sound of it
• Love the German for 'river'!
• River flowing into the Baltic
• It flows one way so as to do it again the other way
• Part of the German/Polish border
• That's the river that sounds as if it's not nice to be near