Stillwater · Limestone · North Wales / Anglesey

Llyn Cefni Reservoir

Evening light on Llyn Cefni reservoir, Anglesey, calm open water with reedy shoreline in September.
Contributor photo

Llyn Cefni at dusk

Kingy79 - CC BY-SA 4.0

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

Fair · Rainbow
Diawl Bach · 12-14
Fairlive now
Tougher conditions for Llyn Cefni Reservoir today — adapt your approach
Useful ripple, fishable wave. Worth a session if the wind holds.
54% confidence
What moved it
  • WindSW 28 km/hModerate breeze
Today’s fly
Diawl Bach
Diawl Bach12-14
Washing-line, sub-surface
Conditions on the water
Live gauge
Wind
Moderate breeze
SW 28 km/h
N
SW
from the south-west
Wave60 cm wave
Water temp—
Air temp17°C
CloudBroken
Pressure1019 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. Damsel Nymph may also come into play as the day develops.
Where
Start with Diawl Bach (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 Diawl Bach (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

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

Watch for Murrough towards evening — this could be the best window of the day.

Bank, sheltered shores

In wind, bank fish the lee shore — boats can anchor in productive areas if conditions allow.

Through the year
0–3 scale · July 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
What's coming
Plan ahead
5-day outlook
Condition match
60%
Cloud100%
Wind30%
Temp60%

A reasonable day here, though wind isn't quite in the sweet spot.

Other water nearby · 5
Llyn Coron
10 km
Brown trout · Rainbow trout
Llyn Padarn
21 km
Brown trout · Arctic char
Llyn Cwellyn
25 km
Brown trout · Arctic char · Salmon
Llyn Cwm Silyn
27 km
Brown trout · Arctic char
Llyn y Dywarchen
27 km
Brown trout · Rainbow trout
Gallery · 3
  1. Evening light on Llyn Cefni reservoir, Anglesey, calm open water with reedy shoreline in September.
    Llyn Cefni at dusk
  2. Open water of Cefni Reservoir across the broad flat surface in winter light.
    Cefni Reservoir
  3. 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
  • Wind conditions (windy) are not ideal for this water.
  • Cloud cover (cloud) suits the fishery well.
  • Buzzer is in its seasonal window, boosting the chance of targeted feeding.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout15 March → 5 October
Related guides
Big Stillwater Playbookreservoir tacticsReservoir Entomologymatching the hatchThermal Layers & Troutreading depth and temperature
Booking & contacts