Possible Clues:

• 18 (11) is what happens to fish
• Occasion to fish before nightfall
• Slack water at dusk
• Of late this could not be the odd ebb or flow
• Of late it may happen to die in a twist
• Not the odd ebb and flow of late
• Of late, neither spring nor neap
• Happening to die out rather late in the day
• There's a regular stream at day's end
• Balanced diet set out for latter part of day