Riaño is the kind of water that makes you stop and look before you fish it, which on a reservoir this size is no small admission. They flooded the old town in the 1980s and the Esla backed up into a long blue arm under the Picos de Europa; the brown trout that live there now have a great deal of room and not much reason to hurry. It fishes like a small inland sea — you really do want a boat, because the best water sits well off the bank, out where the drowned river channel runs. Drift a team of wets, hang buzzers in the calm, or work the drop-offs deep on a bright day. There are pike in here too, which is a complication best kept in the margins of the conversation.

• Reservoir
• Limestone