The Dessoubre is what you end up talking about after a few glasses of wine at the gîte, because you've run out of polite things to say about the Loue. It rises cold and clean out of the Jura plateau, runs for forty-odd kilometres through a steep limestone valley, and joins the Doubs at St-Hippolyte having done almost everything right. The trout are wild, the grayling are properly big, and the hatches are dense enough to make you grateful you brought reading glasses for your fly box. It was hit hard in the early 2000s by the same mix of agricultural runoff and mysterious fish-kill events that savaged the Loue, and the river still has its difficult days. But when it's on — a cool May morning with BWOs coming off a flat glide — it's as good as continental Europe gets, and you leave promising yourself you'll tell no one about it.

• Limestone