The Valserine is the Jura river that doesn't quite fit. It rises in the Pays de Gex, runs south through a deep wooded valley inside the Parc Naturel Régional du Haut-Jura, and joins the Rhône at Bellegarde. It's not quite a limestone spring stream — the geology is mixed, the flow responds to rain more than a pure karst river should — but it isn't a rough freestone either. Think of it as a limestone-influenced mountain river with the best of both worlds: cold, oxygenated water, strong hatches, wild trout of decent average size, and a valley handsome enough to justify the drive even on a blank day. The upper river above Mijoux is small and intimate; the middle reaches around Champfromier open into runs and riffles you can fish with a team of nymphs or a high-floating dry. Grayling are present but not the main event — this is primarily a brown trout river, and the trout are among the best-behaved in the region. They come to a drifted dun without pretending they've never seen one before.

• Limestone