A southerly has held for 17 hours, running colder than the water (6°C air against 10°C water). The end it blows into is taking that chilled surface water, so try the sheltered southern end instead — off the back of the wind, where the undertow returns food along the bottom. That chill sits in the top of the water, though, and the bed is slower to feel it — on a bottom bait it is the undertow, not the temperature, that puts you at this end. Treat it as a tiebreaker between good swims rather than an override — features and angling pressure usually count for more.
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.
Slow down everything. A booby on a fast-sinking line, left static, can pick up deep fish.
Keep an eye on changing conditions — wind shifts and cloud breaks can trigger short feeding spells.
Bank-only venue. Fish from accessible margins, points, weed edges, and inflows.
Hatch predictions
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Hatch predictions
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Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Fly recommendations
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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.
Conditions are away from Llyn Cefni Reservoir's sweet spot — it usually fishes best in ripple wind with cloud skies.
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.
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
Llyn Cefni is Anglesey's second principal stillwater — a modest reservoir managed for public fly fishing.
A southerly has held for 17 hours, running colder than the water (6°C air against 10°C water). The end it blows into is taking that chilled surface water, so try the sheltered southern end instead — off the back of the wind, where the undertow returns food along the bottom. That chill sits in the top of the water, though, and the bed is slower to feel it — on a bottom bait it is the undertow, not the temperature, that puts you at this end. Treat it as a tiebreaker between good swims rather than an override — features and angling pressure usually count for more.
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.
Slow down everything. A booby on a fast-sinking line, left static, can pick up deep fish.
Keep an eye on changing conditions — wind shifts and cloud breaks can trigger short feeding spells.
Bank-only venue. Fish from accessible margins, points, weed edges, and inflows.
Hatch predictions
Top nymph shown — see all 2 guilds as a supporter.
Start free trial14-day free trial. Cancel anytime.
Hatch predictions
Top prey shown — see all 5 as a supporter.
Start free trial14-day free trial. Cancel anytime.
Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.
Fly recommendations
Point fly shown — supporters see the whole team, sizes and why.
Start free trial14-day free trial. Cancel anytime.
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.
Conditions are away from Llyn Cefni Reservoir's sweet spot — it usually fishes best in ripple wind with cloud skies.
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.
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
Llyn Cefni Reservoir is a reservoir in North Wales / Anglesey. The catchment geology is recorded as limestone, and the water sits at about 11 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–June, September. Core methods listed: bank buzzer; nymph; small wet fly. Its Water Framework Directive ecological status is recorded as moderate. Nearby waters in our listings include Llyn Coron at 10 km, Llyn Coron at 10 km and Llyn Alaw at 10 km.
