Stillwater · Granite · North Wales / Gwynedd, GB-WLS

Llyn Trawsfynydd Reservoir

Llyn Trawsfynydd from the shore, open water filling the foreground with moorland hills beyond.

Llyn Trawsfynydd sits high in Snowdonia — a dramatic, wind-blown upland water surrounded by moorland and crag.

Closed season · Rainbow
Booby · 10–12
Closed season
Season reopens 15 March. Try elsewhere.
Closed — confidence not applicable today.

Llyn Trawsfynydd Reservoir is often best in spring through autumn.

What moved it
  • WindS 9 km/hLight breeze · Gusts to 25 km/h
Today's fly
Booby
Booby10–12
Washing-line, sub-surface
Conditions on the water
Estimate
Wind
Light breeze · Gusts to 25 km/h
S 9 km/h
N
S
from the south
WaveRipple
Water temp6.9°C
Air temp1°C
CloudBroken
Pressure1017 hPa
Rain · recent0.0 mm

No gauge on this water — readings are regional estimates from weather, not a live gauge.

How to fish it · for Rainbow
When
Current conditions suit Llyn Trawsfynydd Reservoir well for winter tactics. The ripple should help fish move and feed more confidently.
Where
Start with Autumn Buzzer (12–14) — on the bob / top dropper — slow figure-of-eight retrieve. Early in the day, try buzzers on a slow figure-of-eight or a booby on a fast-sink line near the bottom. Rainbows respond to more active retrieves — try short strips between pauses.
The plan
Plan A

Start with Autumn Buzzer (12–14) — on the bob / top dropper — slow figure-of-eight retrieve. Early in the day, try buzzers on a slow figure-of-eight or a booby on a fast-sink line near the bottom. Rainbows respond to more active retrieves — try short strips between pauses.

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.

Bank

Bank-only venue. Fish from accessible margins, points, weed edges, and inflows.

Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 2 guilds as a supporter.

Start free trial

14-day free trial. Cancel anytime.

Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 4 as a supporter.

Start free trial

14-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
Bloodworm
Not in this water's box
#10
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 trial

14-day free trial. Cancel anytime.

Ranked for today
Rainbow fly box

Boat-friendly, competition-influenced, often wind-driven, with strong top-of-water periods but also classic deep searching and washing-line phases.

What's coming
Plan ahead
5-day outlook
Condition match
88%
Cloud100%
Wind100%
Temp60%

Conditions are ideal for Llyn Trawsfynydd Reservoir — wind, cloud and temperature all line up.

Other water nearby · 5
Llyn Trawsfynydd Reservoir
< 1 km
Brown trout · Rainbow trout
Afon Prysor
1.0 km
Brown trout
Llyn Eiddew Bach
5.0 km
Brown trout
Llyn Eiddew Mawr
6.0 km
Brown trout
Llyn Tecwyn Uchaf
6.0 km
Brown trout · Rainbow trout
Gallery · 6
  1. Llyn Trawsfynydd from the shore, open water filling the foreground with moorland hills beyond.
    Llyn Trawsfynydd
  2. Llyn Trawsfynydd, Gwynedd — a still lake view with open water and the surrounding upland landscape.
    Llyn Trawsfynydd
  3. Llyn Trawsfynydd lake shore with open water and moorland backdrop under an overcast Welsh sky.
    Llyn Trawsfynydd
  4. The southern end of Llyn Trawsfynydd, open water, a grassy shoreline and the Rhinogydd hills beyond.
    The south end of Llyn Trawsfynydd
  5. Shoreline fishing spot on Trawsfynydd Lake in Snowdonia, North Wales
    A fishing area on the shore of Llyn Trawsfynydd, Gwynedd
  6. Terrain map of the venue
    Terrain map
About this water

The isolation and altitude give it a genuine mountain-water atmosphere. Wild and stocked trout inhabit the water; the scenery is spellbinding. Spring and early summer (April–May) see the best hatches — small olives and early buzzers. The granite moorland setting means soft, slightly acidic water and fast clearing after rain, so lure fishing can be briefly productive after spates. This is a place where you go for the surroundings as much as the sport — the kind of water that teaches you patience and presence.

Surface area
4.8 km² (1,186 acres)
Mean depth
about 8.4 m (28 ft)
Length
4.4 km (2.7 mi)
Width
2.3 km (1.4 mi)
Area, mean depth (volume ÷ area), length and width: Wikipedia, Llyn Trawsfynydd
  • Reservoir
  • Granite
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown
What this classification means

NRW WFD Cycle 3 (lake) — Llyn Trawsfynydd: Moderate ecological status. Re-tagged 2026-06-18 from a Dwyryd river reach to the reservoir's own lake waterbody. Source: NRW DataMapWales WFD Cycle 3 classification layer.

NRW (Wales) · GB31034870

Why this score
  • Wind conditions (ripple) closely match what this water fishes best in.
  • Cloud cover (cloud) suits the fishery well.
  • Reservoirs of this kind fish hard at this time of year.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 15 March → 5 October
Related guides
Fly Fishing in North and Mid Walesfeatured in this guideBig Stillwater Playbookreservoir tacticsReservoir Entomologymatching the hatch
Casting instructors near here
Booking & contacts
Boards & regulators
At a glance

Llyn Trawsfynydd Reservoir is a reservoir in North Wales / Gwynedd. The catchment geology is recorded as granite, and the water sits at about 163 m above sea level. Species listed for this water: brown trout and rainbow trout. The trout season is recorded as running from 15 March to 5 October. Best window recorded for anglers: April–May, September. Core methods listed: bank nymph; small wet fly; dry fly (spring olives). Its Water Framework Directive ecological status is recorded as moderate. Nearby waters in our listings include Llyn Trawsfynydd Reservoir at < 1 km, Afon Prysor at 1.0 km and Llyn Eiddew Bach at 5.0 km.