This colour slide is simply marked 'Ramsey' and I assume it is the town of Ramsey near Peterborough. I've looked on the modern day, street view and I can't see this river, although there is a waterway marked and the town is in the fens so I guess this is the right location.
The date this photo was taken is sometime in the 1950s, dated by being in with other slides that had that date marked on them.