Stoneflies
Gammarids
- Ecology: Moderate
- Chemical: Unknown
NRW (Wales) · UKGB110065053960
Rules at a glance
- Fly only
Water temperature for Sea Trout
Ideal12°C est.ideal 8–15°C
0°14°28°
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 — water temperature is working for you, but insect activity is the limiting factor today.
Likely species
Hatch timeline · todayPeak at 11 Uhr
Hatch predictions
Today's headline hatch shown — see all 12 active hatches hour by hour as a supporter.
Start free trial14-day free trial. Cancel anytime.
Sub-surface · on the nymphunder the surface
Hatch predictions
Top nymph shown — see all 3 guilds as a supporter.
Start free trial14-day free trial. Cancel anytime.
Beyond the hatch · worth watchingambient prey(1)
Hatch predictions
Supporters see what else is on the menu.
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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 · October 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
Fly box · Sea Trout
Top
1-2 inch · Tube
In deep pools and dark water, silhouette and contrast do the work colour cannot. A fly that reads as black against depth is enough. Fish it broadside, hold the swing, let it hang at the dangle — that is when the best fish take.
8-12 · Streamer
Slim and mobile — fished sunk through the pool when surface work is not producing. Consistently takes fish that will not come to the surface.
2-4 inch · Streamer
A mobile eel-like profile that undulates through deep pools — effective when sea trout are lying deep and not responding to conventional wets.
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Gallery · 2
IMGP8547 Terrain map
Water quality (WFD)
Why this score · for Sea Trout
- Temperature10028% weight
- Flow8022% weight
- Clarity8518% weight
- Feeding Time5013% weight
- Pressure857% weight
- Insect activity4412% weight
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
Boards & regulators
Glaslyn
Water temperature for Sea Trout
Ideal12°C est.ideal 8–15°C
0°14°28°
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 — water temperature is working for you, but insect activity is the limiting factor today.
Likely species
Hatch timeline · todayPeak at 11 Uhr
Hatch predictions
Today's headline hatch shown — see all 12 active hatches hour by hour as a supporter.
Start free trial14-day free trial. Cancel anytime.
Sub-surface · on the nymphunder the surface
Hatch predictions
Top nymph shown — see all 3 guilds as a supporter.
Start free trial14-day free trial. Cancel anytime.
Beyond the hatch · worth watchingambient prey(1)
Hatch predictions
Supporters see what else is on the menu.
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 · October 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
Fly box · Sea Trout
Top
1-2 inch · Tube
In deep pools and dark water, silhouette and contrast do the work colour cannot. A fly that reads as black against depth is enough. Fish it broadside, hold the swing, let it hang at the dangle — that is when the best fish take.
8-12 · Streamer
Slim and mobile — fished sunk through the pool when surface work is not producing. Consistently takes fish that will not come to the surface.
2-4 inch · Streamer
A mobile eel-like profile that undulates through deep pools — effective when sea trout are lying deep and not responding to conventional wets.
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Gallery · 2
IMGP8547 Terrain map
Water quality (WFD)
- Ecology: Moderate
- Chemical: Unknown
NRW (Wales) · UKGB110065053960
Why this score · for Sea Trout
- Temperature10028% weight
- Flow8022% weight
- Clarity8518% weight
- Feeding Time5013% weight
- Pressure857% weight
- Insect activity4412% weight
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
Boards & regulators