We did this lock - the Anyho weir lock, and a cousin, the Shipton weir lock, on the way into and out of Oxford city. Weir locks are at the end (or start!) of a stretch where the canal and river either share a course or are very close to each other. This lock is four narrowboats wide and very shallow, so it takes in the same amount of water as a narrow lock four times as deep, but does it very (very) slowly with only one sluice paddle on each of the top and bottom gates. This manages the river current and potentially high river levels from flooding the canal or boats in the lock. As we come into this sort of lock, we see signs indicating the river levels - red for flooding, amber for caution and green for safe levels. Though August was horribly dull and wet, the Cherwell, along which the Oxford canal travels for quite a while, showed green.
