Possible Clues:

• Dismissed trip over river mouth
• Where water goes, but not in autumn ...
• Where drain empties
• Waste stream's discharge point
• In winter after this discharge
• One gets a discharge from this, but not in Autumn
• Not in the autumn do you get this at the end of the river
• Drain flowing into a river
• Where, eg, drain enters a river
• Efflux