Spate · Slate · North West Wales / Gwynedd / Eryri, GB-WLS

Glaslyn

A rocky river gorge with large boulders in low, clear water, flanked by wooded hillsides, on the Afon Glaslyn near Aberglaslyn.

Eryri water of the proper romantic kind — out of Llyn Dinas under Yr Wyddfa, through the Aberglaslyn pass, and down to Tremadog Bay at Porthmadog.

Good · Brown Trout
Hare's Ear Nymph · 12-16
Goodlive now
A proper day on the water
River steady at a fishable height. A proper day for it. Work the seams with an upstream nymph, switch to the dry when they show.
90% confidence
What moved it
  • Level0.63 mLast reading 16h ago
  • Water temp17.4°C
  • ClarityClear
Today's fly
Hare's Ear Nymph
Hare's Ear Nymph12-16
Upstream, sub-surface
Conditions on the water
Live gauge
Level
Steady
0.63 m
Last reading 16h ago
Water temp17.4°C
ClarityClear
Weather16°C
WindN 19 km/h
Pressure1025 hPa
Rain · recent3.0 mm
Rain · ahead0.0 mm

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

Water temperature for Brown Trout
Warm — slow
17°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
Good — water clarity is right today, though water temperature could be better.
Hatch timeline · todayPeak at 6am

Hatch predictions

Today's headline hatch shown — see all 9 active hatches hour by hour with Pro.

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Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 4 with Pro.

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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 · 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
March BrownHatch
2
3
2
CapererHatch
2
3
3
2
Heather FlyHatch
2
2
Autumn DunHatch
2
3
2

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Brown Trout fly box

Wild-river first principles. Early-season nymphs and practical searching, then dry flies, emergers and spiders as hatches and surface activity improve.

What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Dwyryd
9.0 km
Brown trout · Salmon · Sea trout
Dwyfor / Dwyfach
14 km
Brown trout · Salmon · Sea trout
Afon Prysor
14 km
Brown trout
Artro
17 km
Brown trout · Salmon · Sea trout
Seiont
18 km
Brown trout · Salmon · Sea trout
Gallery · 2
  1. A rocky river gorge with large boulders in low, clear water, flanked by wooded hillsides, on the Afon Glaslyn near Aberglaslyn.
    IMGP8547
  2. Terrain map of the venue
    Terrain map
About this water

Eryri water of the proper romantic kind — out of Llyn Dinas under Yr Wyddfa, through the Aberglaslyn pass, and down to Tremadog Bay at Porthmadog. The Glaslyn is one of the recognised North Wales sewin rivers and a true spate stream — response time around three hours, levels swinging hard with the Snowdonia weather. NRW data is sobering: salmon at risk with a downward trend. Treat the river accordingly — the fish need every consideration. Slate and schist bedrock underlie this river. Atlantic salmon are under serious conservation pressure — Natural Resources Wales mandates catch-and-release for salmon on all rivers, so all fish must be returned.

Sea trout here

Summer-autumn runs (June–September), primarily nocturnal

  • Slate
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown

NRW (Wales) · UKGB110065053960

The full read · show the working · for Brown Trout · confidence 90%
How the 72 is built — score × weight = contribution
Temperature56 × 28%15.7
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time65 × 13%8.5
Pressure80 × 7%5.6
Insect activity67 × 12%8.0
Conditions total= 73
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
Apple MapsGoogle Maps
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.

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Yorkshire & SpidersNorth Country methodsEuro Nymphingsubsurface methods
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