While flying practice approaches at Sioux City, Iowa I heard:
Tower:
"Skylane Eight Seven Charlie, cleared for the approach; caution, waterfall in the area."
[a short silence, presumably while the Skylane pilot questioned passengers on the transmission]
Skylane:
"Eight Seven Charlie, say again?"
Tower:
"Skylane Eight Seven Charlie, cleared for the approach; caution, waterfall in the area."
[again, a short silence]
Skylane:
"Ah, cleared for the approach – but what do you mean by the waterfall caution?"
Tower:
"Waterfall. You know, ducks and geese – water fowl."
Larry Gerek
Omaha, Nebraska