Spate · Slate · North West Wales / Gwynedd / Eryri

Glaslyn

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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.

Species

A good day — worth the effort

River steady at a fishable height. A reliable day. Match the water height and fish well.

75% confidence in this read
Water temperature for sea trout
Ideal
10°C est.ideal 8–15°C
0°14°28°
Why this score · for sea trout
  • Temperature10028% weight
  • Flow8022% weight
  • Clarity8518% weight
  • Feeding Time5013% weight
  • Pressure857% weight
  • Prey Activity5112% weight
Conditions
Level
0.67 m
Water temp
9.8°C
Estimated
Clarity
Clear
Air temp
16°C
Wind
E 10 km/h
Light breeze
Pressure
1030 hPa
Rain · 24h
0.0 mm
No rain
Rain · ahead
0.1 mm
No meaningful rain · next 48h

Live readings — water temperature is an estimate where the gauge does not record it.

How to fish it · for sea trout
When
May through September; July prime. Night work from full dark once water reaches 13°C; daytime sport on a falling, coloured spate. NRW At Risk — catch-and-release as default.
Where
Lower Glaslyn pool tails through the meadows above Porthmadog; the deeper pots below the Aberglaslyn pass on higher water. Walk the beat in daylight; the boulders are unforgiving in the dark.
Method
Small wets — size 10 to 12 Medicine, Peter Ross, Teal Blue and Silver — across-and-down on a floating line. On falling water carry a sink-tip for the deeper pots. Fish methodically from the tail of each pool; the take comes on the swing.
Kit
9 to 10 ft #6/7, floating line plus a light sink-tip in the bag. 8 to 10 lb fluoro. The river is small enough to wade carefully between casting positions.
Why this works
Good conditions. Temperature is favourable (100), Feeding time is weakest (50). ⏰ Sea trout become most active after dark, but this stretch closes at 21:10 — before that window fully opens. Fish hard in the last legal hour: overcast skies and warm evenings can bring fish on early even in fading light.
Through the year
0–3 scale · May 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
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.

Directions
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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
Seasons & zones
  • Salmon1 April → 17 October
  • Sea trout3 March → 17 October
  • Trout3 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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