- Ecology: Good
- Chemical: Unknown
WFD classification · ES018MSPFES078MAR000050
Rules at a glance
- Public water
- Licence required
Water temperature for Brown Trout
Ideal16°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.
Hatch timeline · todayQuiet day
Hatch predictions
See the full hour-by-hour hatch timeline with Pro.
Start free trial14-day free trial. Cancel anytime.
Sub-surface · on the nymphunder the surface
Hatch predictions
See the full sub-surface read with Pro.
Start free trial14-day free trial. Cancel anytime.
Evidence
Survey-backed · regionalHigh confidence
Backed by regional invertebrate surveys; no sampling on this exact reach yet.
Through the year
0–3 scale · August 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
Gallery · 2
The Río Asón winding through the Ruesga valley, Cantabria Terrain map
Water quality (WFD)
The full read · show the working · for Brown Trout · confidence 50%
How the 0 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow15 × 22%3.3
Clarity95 × 18%17.1
Feeding Time40 × 13%5.2
Pressure80 × 7%5.6
Insect activity11 × 12%1.3
Limiting factor: River is stable — Brown Trout prefers medium flow= 61
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
A drop and clear would lift the flow and clarity scores.
The dawn and dusk windows score higher than the midday lull.
Directions
Seasons & zones
- Trout third Sunday of March → 31 July
Sea trout: Variable seasonal (2026)
Related guides
Booking & contacts
Asón
Water temperature for Brown Trout
Ideal16°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.
Hatch timeline · todayQuiet day
Hatch predictions
See the full hour-by-hour hatch timeline with Pro.
Start free trial14-day free trial. Cancel anytime.
Sub-surface · on the nymphunder the surface
Hatch predictions
See the full sub-surface read with Pro.
Start free trial14-day free trial. Cancel anytime.
Evidence
Survey-backed · regionalHigh confidence
Backed by regional invertebrate surveys; no sampling on this exact reach yet.
Through the year
0–3 scale · August 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
Gallery · 2
The Río Asón winding through the Ruesga valley, Cantabria Terrain map
Water quality (WFD)
- Ecology: Good
- Chemical: Unknown
WFD classification · ES018MSPFES078MAR000050
The full read · show the working · for Brown Trout · confidence 50%
How the 0 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow15 × 22%3.3
Clarity95 × 18%17.1
Feeding Time40 × 13%5.2
Pressure80 × 7%5.6
Insect activity11 × 12%1.3
Limiting factor: River is stable — Brown Trout prefers medium flow= 61
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
A drop and clear would lift the flow and clarity scores.
The dawn and dusk windows score higher than the midday lull.
Directions
Seasons & zones
- Trout third Sunday of March → 31 July
Sea trout: Variable seasonal (2026)
Related guides
Booking & contacts