Well, in this particular photo, I quite like the stop action of the water, we see the silky effect so often (and I am forever trying to achieve it, too, mind you), which is NOT how our eyes see flowing water, we more see it like it is shown here, gurgling, reflecting, foaming, bubbling - and I like the fact that we see it here!
As to fill flash: I don't know how far your flash reaches and how effective it could have been. But it could have been an option to be tested on this scene, I think.
The presented edition is way too pale and milky, I think.
I do like the very deep blue of the sky beneath the bridge, though the colour does speak of some underexposure. If at all, you would need to work on this photo in parts, selectively trying to bring out more detail in the shadows here and there, leaving other parts untouched, I guess.