The Adda through Valtellina is proper big-water Alpine trout fishing — wide gravel runs and long glides fed by snowmelt and glacier off the Rhaetian Alps above Bormio, the gneiss and schist bedrock keeping the water hard and clear even after a lift. By the time it reaches the beats around Tresenda and Piateda it's carrying serious numbers of brown trout, marble trout and hybrids, and grayling that fish hard enough to earn their keep. The marble trout is the fish everyone comes for and nobody keeps — it goes straight back here, as everywhere in its native range. Grayling get treated rather more generously than in Trentino, which after a season of blanket no-retention rules feels almost indulgent. The No-Kill fly reaches, marked with blue signage, are where the fishing turns technical: long leaders, careful footwork on smooth cobble, and trout that have already seen most of what's in the box. Vineyard terraces climb the valley sides the whole way down, which is no bad way to spend an August afternoon between fish.

• Gneiss