The cache is not at the posted co-ords. If you try and go there you will either need a boat or you will get wet feet!
To find the location of the cache you need to first complete the Grafham & Grafham Water Adventure Labs (https://adventurelab.page.link/bWmX).
Once you have completed the five lab stages you will have the values of A, B, C, D and E which will enable you to solve the equation below and give you the final co-ordinates for the location of the cache.
N52 18.ABC W000 17.DEB
Please do not remove the cache container so it is there for others to find and enjoy.
Good Luck!