Photo taken 29/07/10 at Woodwalton Fen, Cambs.
I think this is one of the most stunning wildflowers that I've seen. I've not seen it on any of my walks, but came across it when I visited the marvellous Woodwalton Fen nature reserve near Huntingdon (where I now work). It grows beside still and slow-moving shallow water, and flowers between July and August.
Photo taken 29/07/10 at Woodwalton Fen, Cambs.