Previous answer
Hint: This photo shows a derelict looking lock, photographed on 20th September 1972. The lock, is now restored and the scene now looks rather different, but this is Lock 14 on which canal? The brick toll house in the centre of the photo might be a clue.
Answer: This photograph was of Lock 14 on the Cromford Canal at Langley Mill, near the junction of the Cromford, Erewash and Nottingham canals. Replacement gates from the Nottingham Canal are beside the lock being readied for installation as part of restoration by Erewash Canal Preservation & Development Association, which subsequently restored and continues to look after the Nottingham Canal brick toll office (the small red brick building to the right) and swing bridge (far right) at the junction of the Cromford and Nottingham Canals. There is more info here. Friends of the Cromford Canal are working to restore the Cromford Canal further north.
Correctly guessed by: Malcolm Bridge, Tony Clayton, Chris Davey, Brian Ferris, Michael Golds, Jonathan Lisle, John Lower, Andrew Shipman, Doug Swain, Dave Turner and Izzie Turner.