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
Klinkhammer · 14-18
Closed season
Out of season. Try elsewhere.
Closed — confidence not applicable today.
What moved it
  • Level0.50 mLast reading 16h ago
  • Water temp19.2°C
  • ClarityClear
Today's fly
Klinkhammer
Klinkhammer14-18
High-confidence seasonal pick
Conditions on the water
Live gauge
Level
Steady
0.50 m
lowspate
Water temp19.2°C
ClarityClear
Weather23°C
WindE 21 km/h
Pressure1011 hPa
Rain · recent0.4 mm
Rain · ahead7.9 mm

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

Water temperature for Brown Trout
Warm — slow
19°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.
Why this works
Water at 19.2°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Likely species
Caddisflies
Gammarids
Hatch timeline · todayQuiet day

Hatch predictions

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 2 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 · September 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
Water here around 19°C. Nothing cooler within range — carry a thermometer.
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

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.

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 80%
How the 0 is built — score × weight = contribution
Temperature22 × 28%6.2
Flow15 × 22%3.3
Clarity95 × 18%17.1
Feeding Time60 × 13%7.8
Pressure80 × 7%5.6
Insect activity43 × 12%5.2
Limiting factor: River is stable — Brown Trout prefers medium flow= 45
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
Cooler water — back toward the 10–16 °C ideal band — would lift the score and ease welfare.
A drop and clear would lift the flow and clarity scores.
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)

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