Uncaptioned photograph

Could anyone provide information, as to the use of these hoops. There are two corresponding hoops on the opposite side?

Photograph taken by Tony George on 4 February 2021 and was added to the database on Thursday the 4th of February, 2021

Licensed under a Creative Commons Attribution-ShareAlike licence, see the terms of use

This photo is of Stainton Bridge End Bridge No 170 on the Lancaster Canal (Northern Reaches - in water)