Possible Clues:

• Aquatic game birds
• Birds heading to wetlands after low flying
• In West we float casually around river
• In art we represented filthy-sounding birds
• Duck this when it sounds unfit to drink (9)
• By the sound of it, duck into the pond and the pond is dirty
• Does it sound as if it's undrinkable? then duck it
• Type of animals getting wet down in the river?
• Have the ducks made it sound undrinkable?
• Sounds as if it''s not fit for drinking, but one might perhaps duck that