The Lys comes off its own glacier on the southern flank of Monte Rosa, below the Lyskamm, and runs about forty kilometres down through the Gressoney valley before it meets the Dora Baltea at Pont-Saint-Martin. This is proper high-mountain water — white with meltwater by mid-afternoon in summer, better fished early or in the shoulder months when the glacier isn't running hard. The managed reserve above Gressoney-La-Trinité covers about three kilometres at roughly 1,650 metres, stocked weekly with rainbow trout. It opens later than anywhere else in the valley — 1 June, once the worst of the melt has passed — which tells you most of what you need to know about the character of the water. Bring a rod that can handle some current, and don't expect gin clarity; this isn't that kind of river.

• Granite