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I read about it in The Wind in the Willows:
"For a space they hung there, brushed by the purple loose-strife that fringed the bank; then the clear imperious summons that marched hand-in-hand with the intoxicating melody imposed its will on Mole, and mechanically he bent to his oars again."
But it was absent from the riverbanks of my childhood locale (South Derbyshire). I finally found it in my late 20s in Worcestershire.
Lat/Lng: 51.4231, -0.0678
OS grid ref: TQ344711