Water temperature for Brown Trout
Warm — slow21°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 21.4°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · todayQuiet day
Hatch predictions
See the full hour-by-hour hatch timeline with Pro.
Start free trial14-day free trial. Cancel anytime.
Beyond the hatch · worth watchingambient prey
Hatch predictions
Top prey shown — see all 2 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 · July highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
1
Daddy Long LegsHatch
2
3
2
March BrownHatch
2
3
2
GrannomHatch
2
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
Beats · 1
Afon Twrch — Beats 1 & 2 via Fishing PassportAccess varies
Two short day-ticket beats on the Twrch — Beat 1 (¾ mile) and Beat 2 (½ mile) — both double bank.
What's coming
Plan ahead
5-day outlook
Water here around 21°C. Nothing cooler within range — carry a thermometer.
Gallery · 3
The Afon Twrch winding through moorland above Ystradgynlais 
River Twrch looking south downstream from the side of Pen yr Helyg Terrain map
The full read · show the working · for Brown Trout · confidence 80%
How the 19 is built — score × weight = contribution
Temperature11 × 28%3.1
Flow60 × 22%13.2
Clarity95 × 18%17.1
Feeding Time55 × 13%7.2
Pressure80 × 7%5.6
Insect activity52 × 12%6.2
Limiting factor: Water temperature (21.4°C) is outside Brown Trout's preferred range (10–16°C)= 52
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.
The dawn and dusk windows score higher than the midday lull.
Directions
Seasons & zones
- Trout3 March → 30 September
Related guides
Booking & contacts
Afon Twrch
Water temperature for Brown Trout
Warm — slow21°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 21.4°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · todayQuiet day
Hatch predictions
See the full hour-by-hour hatch timeline with Pro.
Start free trial14-day free trial. Cancel anytime.
Beyond the hatch · worth watchingambient prey
Hatch predictions
Top prey shown — see all 2 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 · July highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
1
Daddy Long LegsHatch
2
3
2
March BrownHatch
2
3
2
GrannomHatch
2
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
Beats · 1
Afon Twrch — Beats 1 & 2 via Fishing PassportAccess varies
Two short day-ticket beats on the Twrch — Beat 1 (¾ mile) and Beat 2 (½ mile) — both double bank.
What's coming
Plan ahead
5-day outlook
Water here around 21°C. Nothing cooler within range — carry a thermometer.
Gallery · 3
The Afon Twrch winding through moorland above Ystradgynlais River Twrch looking south downstream from the side of Pen yr Helyg Terrain map
The full read · show the working · for Brown Trout · confidence 80%
How the 19 is built — score × weight = contribution
Temperature11 × 28%3.1
Flow60 × 22%13.2
Clarity95 × 18%17.1
Feeding Time55 × 13%7.2
Pressure80 × 7%5.6
Insect activity52 × 12%6.2
Limiting factor: Water temperature (21.4°C) is outside Brown Trout's preferred range (10–16°C)= 52
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.
The dawn and dusk windows score higher than the midday lull.
Directions
Seasons & zones
- Trout3 March → 30 September
Related guides
Booking & contacts