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

Alwen Reservoir

Wide landscape view of Alwen Reservoir, North Wales, the open water set among upland moorland and hills.

Alwen is a working reservoir on the Hiraethog moors — workhorse water rather than pilgrimage site, but none the worse for it.

Fair · Rainbow
Booby · 10–12
Fairlive now
Reasonable winter fishing likely at Alwen Reservoir
Good wave on — drift country. A useful wave. Work the productive shore.
53% confidence

Alwen Reservoir is often best in spring through autumn.

What moved it
  • WindS 12 km/hLight breeze · Gusts to 18 km/h
Today's fly
Booby
Booby10–12
Washing-line, sub-surface
Conditions on the water
Estimate
Wind
Light breeze · Gusts to 18 km/h
S 12 km/h
N
S
from the south
Wave20 cm ripple
Water temp8.4°C
Air temp2°C
CloudOvercast
Pressure1018 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 Alwen 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. 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 Autumn Buzzer (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

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.

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 5 as a supporter.

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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
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
Black buzzer, orange thorax
Not in this water's box
#10
How to fish it
Intermediate line · let the breeze drift the team, then hang it 15–30 s

Fly recommendations

Point fly shown — supporters see the whole team, sizes and why.

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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
73%
Cloud50%
Wind100%
Temp60%

A good match for Alwen Reservoir — most conditions are close to what it fishes best in.

Other water nearby · 5
Llyn Brenig
3.0 km
Rainbow trout · Brown trout · Pike
Llyn Clywedog (Saron)
7.0 km
Brown trout
Llyn Elsi
16 km
Brown trout
Llyn Bodgynydd
19 km
Brown trout · Rainbow trout
Llyn Bychan
20 km
Brown trout
Gallery · 5
  1. Wide landscape view of Alwen Reservoir, North Wales, the open water set among upland moorland and hills.
    Alwen Reservoir
  2. Llyn Alwen reservoir in Conwy, North Wales, the open water and surrounding landscape in winter light.
    Llyn Alwen
  3. Llyn Alwen reservoir in Conwy, North Wales, the open water and moorland shoreline in winter conditions.
    Llyn Alwen
  4. Alwen Reservoir dam during a spill event, water cascading over the overflow weir.
    Alwen Reservoir dam
  5. Terrain map of the venue
    Terrain map
About this water

Managed by Welsh Water for public fishing, it produces reliable rainbow and brown trout on buzzers and nymphs from spring through to autumn. The smaller scale (compared to Vyrnwy) means fish are concentrated and accessible; bank fishing is the standard method. Olives and buzzers hatch from April, sedges from June. The limestone geology supports consistent fertility. A no-fuss, straightforward day on the water with a realistic chance of sport — exactly what many fly fishers want.

Surface area
1.4 km² (347 acres)
Length
5.0 km (3.1 mi)
Area © OpenStreetMap contributors. Length and width: Wikipedia, Alwen Reservoir
  • Reservoir
  • Limestone
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown
What this classification means

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

NRW (Wales) · GB31133976

Why this score
  • Wind conditions (ripple) closely match what this water fishes best in.
  • Reservoirs of this kind fish hard at this time of year.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 1 January → 31 December
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

Alwen Reservoir is a reservoir in North Wales / Denbighshire. The catchment geology is recorded as limestone, and the water sits at about 361 m above sea level. Species listed for this water: brown trout and rainbow trout. The trout season is recorded as running from 1 January to 31 December. Best window recorded for anglers: April–June, September. Core methods listed: bank buzzer; nymph; dry fly. Its Water Framework Directive ecological status is recorded as moderate. Nearby waters in our listings include Llyn Brenig at 3.0 km, Llyn Clywedog (Saron) at 7.0 km and Llyn Elsi at 16 km.