Possible Clues:

• Suez, for one
• Word with Erie or root
• 6-Across sighting
• Waterway preserve to which a fair number will go
• Érié, e.g.
• Can there be water there before the end of 19 across?
• Locks in there
• Toll site
• Preserve a lake or other stretch of water
• Water-course where a trainee has to follow vessel