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.

Good · Rainbow
Booby · 10-12
Goodlive now
Reasonable autumn fishing likely at Llyn Cefni Reservoir
Water temperature is the limiting factor today, not the wave. Fish dawn or dusk if you go at all, and handle everything with extra care.
70% confidence

Llyn Cefni Reservoir is often best in spring through autumn.

What moved it
  • WindSE 39 km/hStrong breeze
Today's fly
Booby
Booby10-12
Washing-line, sub-surface
Conditions on the water
Estimate
Wind
Strong breeze
SE 39 km/h
N
SE
from the south-east
Wave80 cm wave
Water temp19.5°C
Air temp21°C
CloudOvercast
Pressure1004 hPa
Rain · recent0.0 mm

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

Head to
Wind driftSE wind
North-western end

A southeasterly has held for 6 hours at much the same temperature as the 20°C water. No thermal steer either way, but the drift still stacks food against the north-western end — the bank it is blowing into — so start there. This reads the upper water, though — a bottom bait at range feels it far less than a floater or a fish in the margins. Treat it as a tiebreaker between good swims rather than an override — features and angling pressure usually count for more.

How to fish it · for Rainbow
When
Conditions are not ideal but fishable at Llyn Cefni Reservoir. Very warm conditions — trout have a narrower safe zone of cool, oxygen-rich water. Fish only at first light or last light, use barbless hooks, keep fish in the water during release, and stop if fish struggle to recover.
Where
Start with Diawl Bach (12-14) — on the bob / top dropper — slow figure-of-eight retrieve. 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.
The plan
Plan A

Start with Diawl Bach (12-14) — on the bob / top dropper — slow figure-of-eight retrieve. 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

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 Sedge towards evening — this could be the best window of the day.

Bank

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

Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 5 as a supporter.

Start free trial

14-day free trial. Cancel anytime.

Through the year
0–3 scale · September 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.

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
35%
Cloud50%
Wind30%
Temp25%

Conditions are away from Llyn Cefni Reservoir's sweet spot — it usually fishes best in ripple wind with cloud skies.

Cooler water nearby · 1
Water here around 20°C — probably warm enough to stress Rainbow . These are likely cooler.
Llyn Padarn
21 km
~17°C
Brown trout · Arctic char
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
  • Wind conditions (strong) are not ideal for this water.
  • Buzzer is in its seasonal window, boosting the chance of targeted feeding.
  • Reservoirs of this kind fish well at this time of year.
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
Boards & regulators