- Ecology: Moderate
- Chemical: Unknown
NRW (Wales) · UKGB110065053960
Rules at a glance
- Free fishing
- Fly only
Water temperature for Brown Trout
Warm — slow18°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Through the open trout season. Spring olives later than lowland rivers — the Snowdonia water warms slowly. Summer sedges and beetle falls in the warmer months.
Where
Upper Glaslyn around Beddgelert and the Llyn Dinas inflow. Pocket water and small pools — small-stream scale.
Method
Upstream dry to risers; dry-dropper through the riffles. North Country spider on the swing in cooler water. Spate-driven on falling water — pick the window after rain rather than fishing a flat low river.
Kit
9 ft #4 — Welsh freestone default. Floating line, 9 to 12 ft leader to 4 to 5 lb fluoro. Studded boots — slate slabs run slick.
Why this works
Water at 18.4°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · todayPeak at 6am
Hatch predictions
Today's headline hatch shown — see all 11 active hatches hour by hour with Pro.
Start free trial14-day free trial. Cancel anytime.
Sub-surface · on the nymphunder the surface
Hatch predictions
Top nymph shown — see all 3 guilds 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 · August highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Salmon runRun
1
2
2
2
2
2
1
Sea trout runRun
1
2
2
2
2
2
2
1
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
What's coming
Plan ahead
5-day outlook
Water here around 18°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
IMGP8547 Terrain map
Water quality (WFD)
The full read · show the working · for Brown Trout · confidence 80%
How the 38 is built — score × weight = contribution
Temperature49 × 28%13.7
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time80 × 13%10.4
Pressure80 × 7%5.6
Insect activity56 × 12%6.7
Conditions total= 71
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.
Directions
Seasons & zones
- Salmon 1 April → 17 October
- Sea trout 3 March → 17 October
- Trout 3 March → 30 September
Sea trout: Variable seasonal (2026) — Recognised North Wales sewin river but condition-sensitive rather than guaranteed. NRW 2024 classification: sea trout at risk. Acid flushes, mining legacy and slate spoil shape the water; fast 3-hour spate response makes timing critical.
Salmon: Negligible (2026) — NRW 2024 Glaslyn catchment summary classifies salmon as at risk with a downward trend; sea trout also at risk. Acid-vulnerable soils, mineral workings, slate and quarry legacy, conifer forestry are the documented pressures. All-Wales catch-and-release applies under the 2020–2030 byelaws.
Related guides
Casting instructors near here
Booking & contacts
Glaslyn
Water temperature for Brown Trout
Warm — slow18°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Through the open trout season. Spring olives later than lowland rivers — the Snowdonia water warms slowly. Summer sedges and beetle falls in the warmer months.
Where
Upper Glaslyn around Beddgelert and the Llyn Dinas inflow. Pocket water and small pools — small-stream scale.
Method
Upstream dry to risers; dry-dropper through the riffles. North Country spider on the swing in cooler water. Spate-driven on falling water — pick the window after rain rather than fishing a flat low river.
Kit
9 ft #4 — Welsh freestone default. Floating line, 9 to 12 ft leader to 4 to 5 lb fluoro. Studded boots — slate slabs run slick.
Why this works
Water at 18.4°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · todayPeak at 6am
Hatch predictions
Today's headline hatch shown — see all 11 active hatches hour by hour with Pro.
Start free trial14-day free trial. Cancel anytime.
Sub-surface · on the nymphunder the surface
Hatch predictions
Top nymph shown — see all 3 guilds 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 · August highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Salmon runRun
1
2
2
2
2
2
1
Sea trout runRun
1
2
2
2
2
2
2
1
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
What's coming
Plan ahead
5-day outlook
Water here around 18°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
IMGP8547 Terrain map
Water quality (WFD)
- Ecology: Moderate
- Chemical: Unknown
NRW (Wales) · UKGB110065053960
The full read · show the working · for Brown Trout · confidence 80%
How the 38 is built — score × weight = contribution
Temperature49 × 28%13.7
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time80 × 13%10.4
Pressure80 × 7%5.6
Insect activity56 × 12%6.7
Conditions total= 71
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.
Directions
Seasons & zones
- Salmon 1 April → 17 October
- Sea trout 3 March → 17 October
- Trout 3 March → 30 September
Sea trout: Variable seasonal (2026) — Recognised North Wales sewin river but condition-sensitive rather than guaranteed. NRW 2024 classification: sea trout at risk. Acid flushes, mining legacy and slate spoil shape the water; fast 3-hour spate response makes timing critical.
Salmon: Negligible (2026) — NRW 2024 Glaslyn catchment summary classifies salmon as at risk with a downward trend; sea trout also at risk. Acid-vulnerable soils, mineral workings, slate and quarry legacy, conifer forestry are the documented pressures. All-Wales catch-and-release applies under the 2020–2030 byelaws.
Related guides
Casting instructors near here
Booking & contacts