Clue: River turns entering artificial lake – bridge now abandoned? (7)
Answer: PLAFOND
Explanation: Definition: bridge now abandoned
Reverse of FAL in POND. Chambers says that a pond is "usually artificial", which hadn't occurred to me before. I knew plafond as French for ceiling (confusingly not floor, as it sounds rather like "platform"), but it's also the name of an early ("abandoned") version of the game of Bridge