The Fier cuts through the Bornes and Aravis on its way down towards the Rhône — fast, cold, limestone-clear, and punctuated with gorges that turn casual fishing into a day's expedition. The upper and middle reaches hold wild brown trout in pocket water that rewards the kind of fishing where you can read the seams in your sleep. Standard Alpine drill: heavy nymph, tight line, pick the cushion behind each boulder. Dry fly comes into its own when the olives and caddis are working in the slower pools between the ragged sections. The gorges limit access to specific entry points — the AAPPMA marks them — and once you're in, you may not get out easily, so plan accordingly. The prime window is May through late June. By July the lower reaches warm and the fishing moves upstream.

• Limestone