The Purón is a short limestone stream descending to the coast near Llanes — barely 10 km, but the geology punches above its size. Limestone cobble and bedrock give the river exceptional clarity; even after a summer spate it clears faster than the surrounding slate-fed drainages. The step-pool sequence and confined valley keep gradients steep. Spate events hit hard and recede quickly — the limestone base drains fast rather than sustaining a prolonged rise. On the drop, the pools focus fish. Wading demands respect: polished wet limestone at step lips can be treacherous underfoot.

Wading: Polished wet limestone slabs at step lips

In the mountain-to-sea trout rivers of Asturias, olives and other mayflies do much of the work in spring whenever levels and colour allow, followed by strong evening caddis and steady buzzer life through early and mid-summer, with terrestrials and mixed surface food from wooded, pastoral banks rounding out the diet whenever flows drop back into safe wading range.