This cache is part of the Sezincote Stroll series and you will find introductory series information in the listing for the first cache Sezincote Stroll - 4 Oaks.
You are looking for a green painted clip-lock box
Not "Sur Le Pont"
All of the bridges on the Sezincote Stroll cross various tributaries of the river Evenlode - a well known river in the North Cotswolds that even has a close-by village named after it.
The river meanders down through Oxfordshire to join the Thames just north west of Oxford. The same route is followed by the First Western rail service to Paddington but the river is a tad more reliable.