Spate · Limestone · Cantabria, ES

Asón

An aerial view of the Asón river winding through a green wooded valley with farmhouses and mountains in the background, in Ruesga, Cantabria, Spain.

Probably the best-known eastern salmonid basin in Cantabria.

Poor · Brown Trout
Pheasant Tail Nymph · 14–18
Closed season
Out of season. Try elsewhere.
Closed — confidence not applicable today.
What moved it
  • Level0.74 mLast reading 3h ago
  • Water temp12.6°C
  • ClarityClear
Today's fly
Pheasant Tail Nymph
Pheasant Tail Nymph14–18
High-confidence seasonal pick
Conditions on the water
Live gauge
Level
Steady
0.74 m
lowspate
Water temp12.6°C
ClarityClear
Weather16°C
WindNW 13 km/h
Pressure1011 hPa
Rain · recent14.4 mm
Rain · ahead7.6 mm

The nearest gauge doesn't record temperatures, so we've estimated it — defer to the river keeper's advice.

Water temperature for Brown Trout
Ideal
13°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Nymphing can work through most of the day.
Where
Cover mixed depths.
Method
Start with tight-line nymphs and adjust if fish rise or drift higher.
Kit
9 ft #4 rod, floating line, 12 ft tapered leader to 4–5 lb fluoro tippet.
Likely species
Gammarids
Hatch timeline · todayQuiet day

Hatch predictions

Today's headline hatch shown — see all 5 active hatches hour by hour as a supporter.

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Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 3 guilds as a supporter.

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Evidence
Survey-backed · regionalHigh confidence

Backed by regional invertebrate surveys; no sampling on this exact reach yet.

Through the year
0–3 scale · November highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
1
March BrownHatch
2
3
2
Late March BrownHatch
2
3
2
Large Brook DunHatch
2
3
2
Large StoneflyHatch
2
3
2

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Brown Trout fly box
Permits & access
Permit required — see local rules.
  • Cantabrian fishing licence required
  • Annex-driven basin rules, named no-kill stretches, and coto conditions matter more than generic salmon-river language, so check the exact stretch before travel.
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Gándara
11 km
0
Brown trout
Río Agüera
16 km
0
Brown trout · Sea trout
Río Campiazo
20 km
0
Brown trout · Sea trout
Río Aguanaz
23 km
0
Brown trout
Río Carranza
9.0 km
Brown trout
Gallery · 2
  1. An aerial view of the Asón river winding through a green wooded valley with farmhouses and mountains in the background, in Ruesga, Cantabria, Spain.
    The Río Asón winding through the Ruesga valley, Cantabria
  2. Terrain map of the venue
    Terrain map
About this water

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.

Hatches & food

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
Water quality (WFD)
  • Ecology: Good
  • Chemical: Unknown

WFD classification · ES018MSPFES078MAR000050

The full read · show the working · for Brown Trout · confidence 75%
How the 0 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow40 × 22%8.8
Clarity95 × 18%17.1
Feeding Time55 × 13%7.2
Pressure80 × 7%5.6
Insect activity48 × 12%5.8
Conditions total= 73
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout third Sunday of March → 31 July

Sea trout: Variable seasonal (2026)

Related guides
Fly Fishing Near Santanderfeatured in this guideFly Fishing Near Bilbaofeatured in this guidePyrenees PlaybookSpanish rivers
Booking & contacts
At a glance

Asón is a spate river in Cantabria, Spain. The catchment geology is recorded as limestone, and the water sits at about 101 m above sea level. The river is described as roughly 39 km long. Species listed for this water: brown trout and sea trout. The trout season is recorded as running from third Sunday of March to 31 July. Best window recorded for anglers: April–July for trout, with sea trout adding interest later in the legal season. Core methods listed: dry fly; euro nymphing; wet fly. Level and flow data for this water is linked from 2 gauges. Its Water Framework Directive ecological status is recorded as good. Nearby waters in our listings include Río Carranza at 9.0 km, Gándara at 11 km and Río Agüera at 16 km.