The River Stour takes its time to pass under this magnificent bridge.
Water blur is always a difficult thing to judge. I added a Circular Polariser and 0.9 ND filters and experimented with shutter speeds. At 4 seconds, I think I had the right amount of swirl.
4 secs at f/22, ISO100
0.6 ND Grad + 0.9 ND + Circular Polariser