What you can't see is the river is high enough to be lapping over the riverwalk (which can be seen more clearly in this photograph). What you can see is the high water mark of the most recent flooding. What's difficult to see (but is visible in larger sizes) is the driftwood stuck in the support beams of the bottom of the bridge, which gives you an idea of the water level of last year's floods.
This bridge, by the way, is maybe two miles upriver from this bridge, which gives you an idea how low the water level can go.
I do love rivers. They're schizophrenic.