My local river is a tributary of the Thames, and it isn't superficially all that impressive. A stream, really, quite narrow and shallow. But in the early industrial revolution, it was perfect for the water-powered technology of the time. For a while, it was the most heavily-used industrial waterway in the country. Now all the watermills have gone, it's hard to imagine the industrial powerhouse it used to be, but I think this little leftover weir shows how fast it flows.
This is the idyllic version of the river, running through parkland around the nice home of the businessman who ran the mill here.
And this is the remains of his mill, barely 100 yards away, one of many which went all the way along the river. There's one functioning water wheel on the Wandle, but (clearly) it isn't this one: