Good question Phil.
Looking at this other photo from a different angle, it's technically a weir.
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It was taken on my 50th birthday back in 2003 when we met up with my son, who was at Uni in Sheffield and my parents from Cheshire.
I've got a feeling we might have walked from Monsal Head along the river to Cressbrook and Millers Dale, but I can't pinpoint that weir on any of my maps. I'm sure you'll be able to work out where it is sometime.
Nothing as huge and dramatic as many in here, but Buttermilk Falls in Beaver Falls PA (near Pittsburgh); em10i ,12-45mm, and those metal things you put on the bottom of your shoes so I wouldn't fall on my butt