It is small enough that you could cross most of it in wellingtons, narrow enough that a fifteen-foot cast is sometimes too long, and wild enough that the trout act genuinely surprised to see you. In other words, it is exactly the kind of river that rewards patience and punishes anyone in a hurry. The fishable water is in the Avallon gorge and upstream through the Vallée du Cousin — a deep, shaded cut through oak and beech woodland where the river runs cold and clean over granite bedrock. The trout are wild and modest in size, but the setting is something else entirely: mossy stones, pools like black glass, the occasional rise that makes you wonder how long it took this fish to work out that there was nothing worth eating in the last six flies it inspected. The hatches are dominated by small caddis and the usual Baetis. Fish a short rod, get below the fish, and stay out of their sightline. A good day on the Cousin is a handful of wild browns and a long walk back to the car through woods that smell of river.

• Granite

• Ecology: Moderate
• Chemical: Unknown