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.
Contributor photo

The Río Asón winding through the Ruesga valley, Cantabria

Jesús Gómez Fernández CC BY 4.0

Probably the best-known eastern salmonid basin in Cantabria.

Poor · Brown Trout
Klinkhammer · 14-18
Poorlive now
Not the day for it
River temperature is the limiting factor today, not the flow. This is not the day to push it. Check the thermal advice above before you head out.
90% confidence
What moved it
  • Level0.49 mDropping after lift
  • Water temp23.5°C
  • ClarityClear
Today’s fly
Klinkhammer
Klinkhammer14-18
High-confidence seasonal pick
Conditions on the water
Live gauge
Level
Steady
0.49 m
lowspate
Water temp23.5°C
ClarityClear
Weather28°C
WindNE 14 km/h
Pressure1016 hPa
Rain · recent0.0 mm
Rain · ahead6.3 mm

Live readings only. Trends shown where the gauge supports them.

Water temperature for brown trout
Warm — slow
23.5°Cideal 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 23.5°C. This is the line where catch-and-release kills brown trout. Do not fish for them today.
Sub-surface · on the nymphunder the surface

Hatch predictions

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Evidence
Records-basedModerate confidence

Based on species-occurrence records, not local invertebrate surveys.

Through the year
0–3 scale · July 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
GrannomHatch
2
2
Large StoneflyHatch
2
3
2
Yellow SallyHatch
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.
  • Se requiere licencia de pesca cántabra
  • Las normas de cuenca por anexo, los tramos sin muerte nombrados y las condiciones de coto pesan más que el lenguaje genérico de río salmonero, así que comprueba el tramo exacto antes de viajar.
What's coming
Plan ahead
5-day outlook
Water here at 23.5°C. Nothing cooler within range.
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.

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

WFD classification · ES018MSPFES078MAR000050

The full read · show the working · for brown trout · confidence 90%
How the 0 is built — score × weight = contribution
Temperature0 × 28%0.0
Flow15 × 22%3.3
Clarity95 × 18%17.1
Feeding Time60 × 13%7.8
Pressure80 × 7%5.6
Insect activity50 × 12%6.0
Limiting factor: Water temperature (23.5°C) is outside Brown Trout's preferred range (10–16°C)= 40
Can you trust it?
Water temperaturelive gauge readinggauge
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
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
  • Troutthird Sunday of March → 31 July

Sea trout: Variable seasonal (2026)

Related guides
Pyrenees PlaybookSpanish riversEuro Nymphingsubsurface methods
Booking & contacts