Deep upland water with excellent wild brown trout and stocked rainbows. Boat and bank fishing. Strong competition pedigree. Dramatic scenery with steep valley sides. Good buzzer and sedge hatches.
- Reservoir
- Slate
Rules at a glance
- Day tickets
- Fly only
How to fish it · for Rainbow
When
Late spring start — May through September is the practical window. Buzzers May into June; sedges through summer; lures for the back-end. Mountain weather changes fast.
Where
Open water boat marks; the dam and the deeper bays. Clywedog's depth means fish go down quickly in summer warm.
Method
Floater with buzzers under indicator in late spring; midge-tip in summer; sweeping line with lures when fish hold deep.
Kit
10 ft #7 boat rod; floating, intermediate and fast-intermediate lines; 6 to 8 lb fluoro. Drogue and a long-handled net.
The plan
Plan A
Start with Daddy Long Legs (10–12) on a As per local method. Rainbows respond to more active retrieves — try short strips between pauses. If that does not produce, switch depth or speed before changing the pattern entirely.
Plan B
Slow down everything. A booby on a fast-sinking line, left static, can pick up deep fish.
Watch for
Keep an eye on changing conditions — wind shifts and cloud breaks can trigger short feeding spells.
Either bank or boat
Good ripple suits both bank and boat. Bank: work inflows, dam walls, and points. Boat: broadside drift covering wind lanes.
Sub-surface · on the nymphunder the surface
Hatch predictions
Supporters see the full sub-surface read.
Start free trial14-day free trial. Cancel anytime.
Beyond the hatch · worth watchingambient prey(1)
Hatch predictions
Top prey shown — see all 3 as a supporter.
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Through the year
0–3 scale · November highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
2
1
Reservoir BuzzerHatch
2
3
3
3
3
3
2
Daphnia SwarmHatch
2
3
3
3
2
Lake OliveHatch
2
3
3
3
3
3
2
Silverhorns & LonghornsHatch
1
2
2
2
1
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Buzzer team todayfor the conditions now
Point#10
Bloodworm
Not in this water's box
How to fish it
Slow-sink line · slow figure-of-eight, pausing to let the flies hang
Fly recommendations
Point fly shown — supporters see the whole team, sizes and why.
Start free trial14-day free trial. Cancel anytime.
Ranked for today
Rainbow fly box
Traditional wild-trout llyn fishing. Wet flies and dabblers stay central, with buzzer, caddis, terrestrials and occasional small fry patterns becoming important as the season warms.
10–12 · Pattern
Fish it in the film
What's coming
Plan ahead
5-day outlook
Condition match
64%
Cloud25%
Wind65%
Temp100%
A reasonable day here, though cloud isn't quite in the sweet spot.
Other water nearby · 5
Gallery · 3
Llyn Clywedog Reservoir 
Llyn Clywedog Trout Fishery Terrain map
About this water
Water quality (WFD)
- Ecology: Moderate
- Chemical: Unknown
What this classification means
NRW WFD Cycle 3 (lake) — Llyn Clywedog: Moderate ecological status. Re-tagged 2026-06-18 from an inflow-river reach to the reservoir's own lake waterbody. Source: NRW DataMapWales WFD Cycle 3 classification layer.
NRW (Wales) · GB30937446
Why this score
- Temperature (cool) is in the sweet spot for winter fishing.
- Reservoirs of this kind fish hard at this time of year.
Directions
Seasons & zones
- Trout Late March → Mid October
Related guides
Casting instructors near here
Booking & contacts
Llyn Clywedog
615-acre reservoir in the upper Severn headwaters near Llanidloes.
How to fish it · for Rainbow
When
Late spring start — May through September is the practical window. Buzzers May into June; sedges through summer; lures for the back-end. Mountain weather changes fast.
Where
Open water boat marks; the dam and the deeper bays. Clywedog's depth means fish go down quickly in summer warm.
Method
Floater with buzzers under indicator in late spring; midge-tip in summer; sweeping line with lures when fish hold deep.
Kit
10 ft #7 boat rod; floating, intermediate and fast-intermediate lines; 6 to 8 lb fluoro. Drogue and a long-handled net.
The plan
Plan A
Start with Daddy Long Legs (10–12) on a As per local method. Rainbows respond to more active retrieves — try short strips between pauses. If that does not produce, switch depth or speed before changing the pattern entirely.
Plan B
Slow down everything. A booby on a fast-sinking line, left static, can pick up deep fish.
Watch for
Keep an eye on changing conditions — wind shifts and cloud breaks can trigger short feeding spells.
Either bank or boat
Good ripple suits both bank and boat. Bank: work inflows, dam walls, and points. Boat: broadside drift covering wind lanes.
Sub-surface · on the nymphunder the surface
Hatch predictions
Supporters see the full sub-surface read.
Start free trial14-day free trial. Cancel anytime.
Beyond the hatch · worth watchingambient prey(1)
Hatch predictions
Top prey shown — see all 3 as a supporter.
Start free trial14-day free trial. Cancel anytime.
Through the year
0–3 scale · November highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
2
1
Reservoir BuzzerHatch
2
3
3
3
3
3
2
Daphnia SwarmHatch
2
3
3
3
2
Lake OliveHatch
2
3
3
3
3
3
2
Silverhorns & LonghornsHatch
1
2
2
2
1
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Buzzer team todayfor the conditions now
Point#10
Bloodworm
Not in this water's box
How to fish it
Slow-sink line · slow figure-of-eight, pausing to let the flies hang
Fly recommendations
Point fly shown — supporters see the whole team, sizes and why.
Start free trial14-day free trial. Cancel anytime.
Ranked for today
Rainbow fly box
Traditional wild-trout llyn fishing. Wet flies and dabblers stay central, with buzzer, caddis, terrestrials and occasional small fry patterns becoming important as the season warms.
10–12 · Pattern
Fish it in the film
What's coming
Plan ahead
5-day outlook
Condition match
64%
Cloud25%
Wind65%
Temp100%
A reasonable day here, though cloud isn't quite in the sweet spot.
Other water nearby · 5
Gallery · 3
Llyn Clywedog Reservoir Llyn Clywedog Trout Fishery Terrain map
About this water
Deep upland water with excellent wild brown trout and stocked rainbows. Boat and bank fishing. Strong competition pedigree. Dramatic scenery with steep valley sides. Good buzzer and sedge hatches.
- Reservoir
- Slate
Water quality (WFD)
- Ecology: Moderate
- Chemical: Unknown
What this classification means
NRW WFD Cycle 3 (lake) — Llyn Clywedog: Moderate ecological status. Re-tagged 2026-06-18 from an inflow-river reach to the reservoir's own lake waterbody. Source: NRW DataMapWales WFD Cycle 3 classification layer.
NRW (Wales) · GB30937446
Why this score
- Temperature (cool) is in the sweet spot for winter fishing.
- Reservoirs of this kind fish hard at this time of year.
Directions
Seasons & zones
- Trout Late March → Mid October
Related guides
Casting instructors near here
Booking & contacts
At a glance
Llyn Clywedog is a reservoir in Powys / Upper Severn headwaters, Wales. Its recorded elevation is about 322 m above sea level and the catchment geology is slate. Our data lists rainbow trout and brown trout here. The trout season is recorded as running from Late March to Mid October. Best window recorded for anglers: May to September. Core methods listed: washing line; buzzer; wet fly drift. Its Water Framework Directive ecological status is recorded as moderate. Nearby waters in our listings include Llyn Clywedog at < 1 km, Llyn Bugeilyn at 9.0 km and Llyn Llygad Rheidol at 11 km.