Probably the best-known eastern salmonid basin in Cantabria. Crystal-clear limestone river rising in Picos de Europa karst with exceptional water quality. Heavily managed: cotos, special no-kill trout stretches, protected zones and changing rules by annex. The compact 39 km concentrates excellent fishing with 4-hour spate response. Salmon belong mainly to the river's historical prestige now; wild brown trout in upper sections are the real practical interest for fly anglers, with sea trout adding later-season migratory value. Limestone geology creates characteristic pale turquoise pools ideal for sight-fishing with small nymphs and dries.
In Cantabria's shorter mountain and foothill trout rivers, fish make the most of spring olives and stoneflies in clear windows between freshets, then switch to evening caddis and small buzzers through the warmer months, with terrestrials becoming a key option in sheltered glides and under tree cover once summer settles in.
- Limestone
