Longman Dictionary of Contemporary English
lock keeper
noun
EXAMPLES FROM CORPUS
▪ John Cryer, the lock keeper, and Tom Mercer, the engine driver, are at the left of the picture.
Wikipedia
Lock keeper
A Lock keeper, Lock Tender, or lock operator looks after a canal or river lock, operating it and if necessary maintaining it or organizing its maintenance. Traditionally, the lock keeper lived on-site, often in a small purpose-built cottage. With the decline in commercial traffic the occupation is dying out, at least in Britain. Many previously manned locks are now unmanned.
The Kentucky River Museum is located in a former lock operator's dwelling.