Kevin T of NB Tranquility got it. It is the breather for the ground paddles on a lock on the Huddersfield Narrow Canal. The pepperpot-shaped device seems to serve as a bollard or strapping post too.
This is at Lock 12W.
A computer bug! - Didn't 'alf rain last night. The African Queen came past during a particularly heavy burst. Shame the Captain didn't have a cabin to shelter in, you would ...
36 minutes ago