The Lena runs from Cantabrian limestone and slate country, a responsive river arriving into the Nalón system. The upper reaches show step-pool through mixed limestone and slate; the descent is steep and response to rainfall immediate. The water carries the blended character of both limestone and slate influences. The middle Lena opens into pool-riffle sequences on mixed cobble-gravel. The pools are productive and hold generations of fishing tradition. The river's character throughout is of a responsive Cantabrian system. The wading demands attention in the upper step-pool sections.

Wading: Wet lichen covered boulders

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.