Stillwater · Mixed · Black Mountains, South East Wales (Bannau Brycheiniog / Usk catchment)

Grwyne Fawr Reservoir

Calm reflective water of Grwyne Fawr Reservoir surrounded by grassy Black Mountains hillsides under a partly cloudy sky.

The most remote of Wales's reservoir fisheries — a 30-acre stone dam impoundment high in the Black Mountains, walk-in only, with genuinely wild, unstocked brown trout running small (8oz-2lb) in a dramatic, isolated valley.

Good · Trout
Coch-y-Bonddu Beetle · 10-14
Goodlive now
Evening session looks promising at Grwyne Fawr Reservoir
Good wave on — drift country. Drift fishing weather — three flies on a long leader.
66% confidence

Grwyne Fawr Reservoir is often best in spring through autumn.

What moved it
  • WindNW 16 km/hGentle breeze
Today's fly
Coch-y-Bonddu Beetle
Coch-y-Bonddu Beetle10-14
Upstream dry, on top
Conditions on the water
Estimate
Wind
Gentle breeze
NW 16 km/h
N
NW
from the north-west
Wave20 cm ripple
Water temp—
Air temp13°C
CloudClear
Pressure1025 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 Trout
When
Settled weather with some breeze — this is an exposed, high-altitude water
Where
Start with Bumble (10-12) — on the bob / top dropper. As evening approaches, switch to dries or emergers if you see surface activity.
The plan
Plan A

Start with Bumble (10-12) — on the bob / top dropper. As evening approaches, switch to dries or emergers if you see surface activity.

Plan B

If surface work dries up, try a diawl bach or hare's ear on the point and skate a sedge pattern on the bob at last light.

Watch for

Evening tends to be the best period in summer — stay late if you can for a sedge or spinner fall.

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 4 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
Heather FlyHatch
2
2
Daddy Long LegsHatch
2
3
2
Claret DunHatch
2
3
2
Murrough (Great Red Sedge)Hatch
2
3
2

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Trout fly box

Traditional wild-trout llyn fishing. Wet flies and dabblers stay central, with buzzer, caddis, terrestrials and occasional small fry patterns becoming important as the season warms.

Bays & launches · 1

Walk-in only — nearest car park is Blaen-y-Cwm, with a track following the Grwyne Fawr river up the valley to the reservoir.

Glanusk EstateEnquiry
Remote, unstocked wild brown trout water controlled by the same estate that holds Usk river beats downstream.
Visit official site ↗
What's coming
Plan ahead
5-day outlook
Condition match
52%
Cloud25%
Wind65%
Temp60%

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

Other water nearby · 5
Llynfi
8.0 km
Brown trout · Grayling · Chub
Brynhenllys Fishery
11 km
Brown trout
Talybont Reservoir
18 km
Brown trout
Llyn Cwm Llwch
24 km
Brown trout
Beacons Reservoir
27 km
Brown trout · Rainbow trout
Gallery · 2
  1. Calm reflective water of Grwyne Fawr Reservoir surrounded by grassy Black Mountains hillsides under a partly cloudy sky.
    Grwyne Fawr Reservoir
  2. Terrain map of the venue
    Terrain map
About this water

The most remote of Wales's reservoir fisheries — a 30-acre stone dam impoundment high in the Black Mountains, walk-in only, with genuinely wild, unstocked brown trout running small (8oz-2lb) in a dramatic, isolated valley. The dam itself is worth knowing the story of: authorised by an Act of Parliament in 1910, it took 16 years to build (delayed by the First World War) via a 12-mile narrow-gauge railway that was reportedly never formally approved for its route, serving a workers' settlement nicknamed 'Tin Town' that housed up to a thousand people and was dismantled within weeks of the dam's completion in 1928. It's now controlled by Glanusk Estate, the same estate that holds Usk river water downstream.

  • Reservoir
  • Mixed
Why this score
  • Sedge is in its seasonal window, boosting the chance of targeted feeding.
Related guides
Scotland Playbookloch & river fishingThermal Layers & Troutreading depth and temperatureEuro Nymphingsubsurface methods
Casting instructors near here
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