Related Clues:

• See 23-Down
• Ocean motion
• Ebb and neap, e.g.
• Neap and ebb
• They may crash and break
• Surges
• Surfer's need
• Potential sandcastle destroyers
• High and low, e.g.
• Signals goodbye
• Surfer's concern
• Permanent features
• Bay of Fundy attractions
• Ebb and others
• Don't make them!