Cwm Silyn is a remote upland llyn in a glacial cwm beneath the Nantlle Ridge crags, west of Snowdon — ten hectares of wild brown trout and a relict Arctic char population. A mile's walk from Llanllyfni and you're somewhere a Welsh fly fisher would call proper mountain water. The SGLL ticket covers it; the char take a four-fish daily limit alongside the regular trout bag.
A patient day, if you fancy it
Glassy and bright — hard work without a breeze. A flat lough is a quiet lough — wait for the breeze.
35% confidence — limited data
Wind 40 km/h — strong wind on open water. Use caution afloat; sheltered bays recommended.
Live now
Conditions on the water
Trends shown where the gauge supports them
Wind
SW 40 km/h
Strong breeze
Wave
80 cm wave
Water temp
—
No reading
Air temp
11°C
Cloud
Overcast
Pressure
992 hPa
Rain · 24h
0.0 mm
No rain
Some readings unavailable — check directly before fishing.
How to fish · for brown trout
The brief
When · where · method · kit
How to fish it · for brown trout
When
The buzzer is on. Sedge may also come into play as the day warms. Strong wind will make open-water drifting difficult. Look for sheltered bays and lee shores. Dusk on the lake is prime time for surface feeding — stay out as long as light allows.
Where
With limited drift, anchor or fish static from sheltered positions. Work Pheasant Tail Nymph on the bob and Diawl Bach on the point.
Today's tactical plan
The plan
Plan A · Plan B · what to watch · bank or boat
The plan
Plan A
With limited drift, anchor or fish static from sheltered positions. Work Pheasant Tail Nymph on the bob and Diawl Bach on the point.
Plan B
If the main plan is not working, switch to a smaller, more imitative pattern fished slower and deeper. A change of drift angle can also make a difference.
Watch for
Evening tends to be the best period in summer — stay late if you can for a sedge or spinner fall.
Bank, sheltered shores
Strong wind makes boat fishing difficult — sheltered bank spots near lee shores will fish best.
Hatches & runs
What's on, when
Twelve months at a glance
Through the year
0–3 scale · June highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Black MidgeHatch
2
3
3
3
3
3
3
3
3
3
3
2
Daddy Long LegsHatch
2
3
2
Murrough (Great Red Sedge)Hatch
1
2
1
Lake OliveHatch
1
2
2
2
2
2
1
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Today's fly · curated pack
Top pattern + the box
6 patterns from this venue's curated pack
Evidence
Why today scores what it does
The factors driving today's verdict
Why this score
- Wind conditions (strong) are not ideal for this water.
- Buzzer is in its seasonal window, boosting the chance of targeted feeding.
Access · 1
Check the current rules, permits and access before travelling.
Day ticket via Fishing PassportSeiont, Gwyrfai a Llyfni (SGLL) Fishing Society (via Fishing Passport)
Wild brown troutArctic char / torgochFlySpinBait
Remote glacial cwm under the Nantlle Ridge — wild brown trout with a relict Arctic char (torgoch) population. 1-mile walk from Llanllyfni. SGLL £25/day ticket covers all SGLL waters.
Day £25, weekly £90 — SGLL ticket covers all Society waters. Up to 4 char/day in the bag limit. EA/NRW rod licence required.
Arrange access →About this water · Lough note · 4 min read
About this water
Llyn Cwm Silyn, on the water
Field guide · contributor-editedLlyn Cwm Silyn · about
What this water is
Background · character · contributors
About this water
Cwm Silyn is a remote upland llyn in a glacial cwm beneath the Nantlle Ridge crags, west of Snowdon — ten hectares of wild brown trout and a relict Arctic char population. A mile's walk from Llanllyfni and you're somewhere a Welsh fly fisher would call proper mountain water. The SGLL ticket covers it; the char take a four-fish daily limit alongside the regular trout bag.
- Lake
- Ordovician volcanics
Llyn Cwm Silyn · directions
How to get to the water
Directions
Llyn Cwm Silyn
Cwm Silyn is a remote upland llyn in a glacial cwm beneath the Nantlle Ridge crags, west of Snowdon — ten hectares of wild brown trout and a relict Arctic char population.
Species
A patient day, if you fancy it
Glassy and bright — hard work without a breeze. A flat lough is a quiet lough — wait for the breeze.
35% confidence — limited data
Wind 40 km/h — strong wind on open water. Use caution afloat; sheltered bays recommended.
Conditions
Wind
SW 40 km/h
Strong breeze
Wave
80 cm wave
Water temp
—
No reading
Air temp
11°C
Cloud
Overcast
Pressure
992 hPa
Rain · 24h
0.0 mm
No rain
Some readings unavailable — check directly before fishing.
Condition match
41%
Cloud70%
Wind30%
Temp25%
Conditions are away from this venue's sweet spot — it usually fishes best in ripple wind with mixed skies.
How to fish it · for brown trout
When
The buzzer is on. Sedge may also come into play as the day warms. Strong wind will make open-water drifting difficult. Look for sheltered bays and lee shores. Dusk on the lake is prime time for surface feeding — stay out as long as light allows.
Where
With limited drift, anchor or fish static from sheltered positions. Work Pheasant Tail Nymph on the bob and Diawl Bach on the point.
The plan
Plan A
With limited drift, anchor or fish static from sheltered positions. Work Pheasant Tail Nymph on the bob and Diawl Bach on the point.
Plan B
If the main plan is not working, switch to a smaller, more imitative pattern fished slower and deeper. A change of drift angle can also make a difference.
Watch for
Evening tends to be the best period in summer — stay late if you can for a sedge or spinner fall.
Bank, sheltered shores
Strong wind makes boat fishing difficult — sheltered bank spots near lee shores will fish best.
Why this score
- Wind conditions (strong) are not ideal for this water.
- Buzzer is in its seasonal window, boosting the chance of targeted feeding.
Through the year
0–3 scale · June highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Black MidgeHatch
2
3
3
3
3
3
3
3
3
3
3
2
Daddy Long LegsHatch
2
3
2
Murrough (Great Red Sedge)Hatch
1
2
1
Lake OliveHatch
1
2
2
2
2
2
1
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Access · 1
Check the current rules, permits and access before travelling.
Day ticket via Fishing PassportSeiont, Gwyrfai a Llyfni (SGLL) Fishing Society (via Fishing Passport)
Wild brown troutArctic char / torgochFlySpinBait
Remote glacial cwm under the Nantlle Ridge — wild brown trout with a relict Arctic char (torgoch) population. 1-mile walk from Llanllyfni. SGLL £25/day ticket covers all SGLL waters.
Day £25, weekly £90 — SGLL ticket covers all Society waters. Up to 4 char/day in the bag limit. EA/NRW rod licence required.
Arrange access →Directions
About this water
Cwm Silyn is a remote upland llyn in a glacial cwm beneath the Nantlle Ridge crags, west of Snowdon — ten hectares of wild brown trout and a relict Arctic char population. A mile's walk from Llanllyfni and you're somewhere a Welsh fly fisher would call proper mountain water. The SGLL ticket covers it; the char take a four-fish daily limit alongside the regular trout bag.
- Lake
- Ordovician volcanics
About this water · Lough note · 4 min read
Cwm Silyn is a remote upland llyn in a glacial cwm beneath the Nantlle Ridge crags, west of Snowdon — ten hectares of wild brown trout and a relict Arctic char population. A mile's walk from Llanllyfni and you're somewhere a Welsh fly fisher would call proper mountain water. The SGLL ticket covers it; the char take a four-fish daily limit alongside the regular trout bag.
Other water nearby · 5