Stillwater · Limestone · North Wales / Anglesey, GB-WLS

Llyn Cefni Reservoir

Open water of Cefni Reservoir across the broad flat surface in winter light.

Llyn Cefni is Anglesey's second principal stillwater — a modest reservoir managed for public fly fishing.

Fair · Rainbow
Diawl Bach · 12-14
Fairlive now
Reasonable summer fishing likely at Llyn Cefni Reservoir
Good wave on — drift country. A useful wave. Work the productive shore.
58% confidence

Llyn Cefni Reservoir is often best in spring through autumn.

What moved it
  • WindN 21 km/hModerate breeze
Today's fly
Diawl Bach
Diawl Bach12-14
Washing-line, sub-surface
Conditions on the water
Live gauge
Wind
Moderate breeze
N 21 km/h
N
N
from the north
Wave40 cm chop
Water temp—
Air temp17°C
CloudBroken
Pressure1021 hPa
Rain · recent0.0 mm

Some readings unavailable — check directly before fishing.

How to fish it · for Rainbow
When
The buzzer is on at Llyn Cefni Reservoir. The ripple should help fish move and feed more confidently. Early morning is often the most productive window in summer — make the most of it.
Where
Start with Diawl Bach (12-14) — on the bob / top dropper — slow figure-of-eight retrieve. Midday in warm weather — switch to a fast-sink or Di-7 and fish boobies or blobs along the bottom. Rainbows respond to more active retrieves — try short strips between pauses.
The plan
Plan A

Start with Diawl Bach (12-14) — on the bob / top dropper — slow figure-of-eight retrieve. Midday in warm weather — switch to a fast-sink or Di-7 and fish boobies or blobs along the bottom. Rainbows respond to more active retrieves — try short strips between pauses.

Plan B

If the main plan stalls, drop to a size 14–16 midge — switch to a washing-line or suspender rig and change drift line before you change food group.

Watch for

Buzzer may strengthen through the middle of the day as conditions warm.

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 with Pro.

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Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 5 with Pro.

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Through the year
0–3 scale · August highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
2
1
Daphnia SwarmHatch
2
3
3
3
2
Daddy Long LegsHatch
2
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.

Ranked for today
Rainbow fly box

More compact-water behaviour, often winter-friendly, with simple lures, blobs, boobies and small naturals all in play depending on water colour and stocking freshness.

What's coming
Plan ahead
5-day outlook
Condition match
86%
Cloud100%
Wind65%
Temp100%

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

Other water nearby · 5
Llyn Coron
10 km
Brown trout · Rainbow trout
Llyn Alaw
10 km
Brown trout · Rainbow trout
Llyn Padarn
21 km
Brown trout · Arctic char
Llyn Cwm Dwythwch
23 km
Brown trout
Llyn Cwellyn
25 km
Brown trout · Arctic char · Salmon
Gallery · 2
  1. Open water of Cefni Reservoir across the broad flat surface in winter light.
    Cefni Reservoir
  2. Terrain map of the venue
    Terrain map
About this water

Llyn Cefni is Anglesey's second principal stillwater — a modest reservoir managed for public fly fishing. It produces solid sport on buzzers and nymphs, with bank access and occasional boat availability. The shallow limestone water means reliable food chains and consistent hatches. Spring and early summer are best; autumn can be productive after a spate. This is a straightforward day-ticket water — no pretense, no drama, just a chance to be on trout in a genuine wild setting. The Anglesey isolation gives even this workhorse water a quiet, undisturbed feel.

  • Reservoir
  • Limestone
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown
What this classification means

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

NRW (Wales) · GB31032926

Why this score
  • Cloud cover (cloud) suits the fishery well.
  • Temperature (cool) is in the sweet spot for summer fishing.
  • Buzzer is in its seasonal window, boosting the chance of targeted feeding.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 15 March → 5 October
Related guides
Big Stillwater Playbookreservoir tacticsReservoir Entomologymatching the hatchThermal Layers & Troutreading depth and temperature
Casting instructors near here
Booking & contacts
Clubs & associations