Spate · Slate · North West Wales / Gwynedd

Mawddach

The Afon Mawddach flowing through the valley at Llanelltyd, looking upriver with wooded hillsides on the banks.

Small Snowdonia spate river with rapid response (3 hours) — quick to rise and quick to fall.

Good · Brown Trout
CDC Emerger · 16-18
Goodlive now
A proper day on the water
Low and clear — careful approach country. Stay small, stay accurate.
90% confidence
What moved it
  • Level0.13 m
  • Water temp17.4°C
  • ClarityClear
Today's fly
CDC Emerger
CDC Emerger16-18
Upstream dry, in the film
Conditions on the water
Live gauge
Level
Steady
0.13 m
Water temp17.4°C
ClarityClear
Weather16°C
WindNE 8 km/h
Pressure1020 hPa
Rain · recent0.0 mm
Rain · ahead0.0 mm

The nearest gauge doesn't record temperatures, so we've estimated it — defer to the river keeper's advice.

Water temperature for Brown Trout
Warm — slow
17°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Through the open trout season. Spring olives April through May; sedges through summer; small dark flies into autumn close. Snowdonia weather changes fast.
Where
Pool tails and pocket water through the Snowdonia spate stretches. Small-river scale — short casts, careful approach.
Method
Upstream dry to risers; dry-dropper through the riffles. North Country spider on the swing in cooler water. Spate-driven on falling water.
Kit
9 ft #4 — Welsh freestone default. Floating line, 9 to 12 ft leader to 4 to 5 lb fluoro. Studded boots — slate slabs run slick.
Why this works
Good — water clarity is right today, though time of day could be better.
Hatch timeline · todayPeak at 6am

Hatch predictions

Today's headline hatch shown — see all 12 active hatches hour by hour with Pro.

Start free trial

14-day free trial. Cancel anytime.

Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 3 guilds with Pro.

Start free trial

14-day free trial. Cancel anytime.

Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 2 with Pro.

Start free trial

14-day free trial. Cancel anytime.

Evidence
Survey-backed · regionalHigh confidence

Backed by regional invertebrate surveys; no sampling on this exact reach yet.

Through the year
0–3 scale · August highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Salmon runRun
1
2
2
2
2
2
2
1
Trout seasonSeason
1
2
2
2
2
2
1
Daddy Long LegsHatch
2
3
2
March BrownHatch
2
3
2
GrannomHatch
2
2
Large StoneflyHatch
2
3
2

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

Ranked for today
Brown Trout fly box

Wild-river first principles. Early-season nymphs and practical searching, then dry flies, emergers and spiders as hatches and surface activity improve.

Beats · 1
River Wnion — Dolgellau AADay tickets
The Mawddach's largest tributary, running from the tidal Junction Pool through Dolgellau town to a narrow, boulder-strewn upland spate fishery.
Visit official site ↗
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Afon Eden (Welsh)
5.0 km
Brown trout
Dysynni
14 km
37
Brown trout · Salmon · Sea trout
Artro
16 km
Brown trout · Salmon · Sea trout
Afon Prysor
17 km
Brown trout
Dovey (Dyfi)
18 km
Brown trout · Salmon · Sea trout
Gallery · 5
  1. The Afon Mawddach flowing through the valley at Llanelltyd, looking upriver with wooded hillsides on the banks.
    The Afon Mawddach at Llanelltyd
  2. The Afon Mawddach at Llanelltyd with the river dominating the foreground and wooded hills beyond.
    The Afon Mawddach at Llanelltyd
  3. The River Mawddach near Ganllwyd on a spring day, clear water over a rocky bed in a wooded valley.
    River Mawddach at Ganllwyd
  4. The Mawddach above Penmaenpool in winter light, a wide flat glide with wooded valley sides rising steeply.
    The Mawddach above Penmaenpool
  5. Terrain map of the venue
    Terrain map
About this water

Small Snowdonia spate river with rapid response (3 hours) — quick to rise and quick to fall. Fish the window when water is in condition. Salmon and sea trout through season; brown trout in upper reaches. Fish sinking-tip with medium tubes for salmon, smaller wets for sea trout. Estuary near Barmouth concentrates migratory fish. Tight timing; wait for rain and be prepared. Slate and schist bedrock underlie this river. Atlantic salmon are under serious conservation pressure — Natural Resources Wales mandates catch-and-release for salmon on all rivers, so all fish must be returned.

Sea trout here

Summer-autumn runs (June–September), primarily nocturnal

  • Slate
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown
What this classification means

NRW WFD Cycle 3 — Mawddach (lower) near Dolgellau: Moderate ecological status. Corrected 2026-06-18 from a Gwynant-tributary tag (was recorded Good). Source: NRW DataMapWales WFD Cycle 3 classification layer.

NRW (Wales) · GB110064048710

The full read · show the working · for Brown Trout · confidence 90%
How the 74 is built — score × weight = contribution
Temperature68 × 28%19.0
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time60 × 13%7.8
Pressure80 × 7%5.6
Insect activity61 × 12%7.3
Conditions total= 74
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
Cooler water — back toward the 10–16 °C ideal band — would lift the score and ease welfare.
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Salmon 20 March → 17 October
  • Trout 3 March → 30 September

Sea trout: Variable seasonal (2026) — NRW At Risk classification. Small Snowdonia spate river where sea trout and salmon share the system. Fast response (3h) means windows after rain are brief but productive when they come. Stocks are down from historical levels.

Salmon: Negligible (2026) — NRW / EA 2024 Salmon Stocks Assessment classifies this Welsh principal salmon river 'at risk' — egg deposition below Conservation Limit. All Wales byelaws (in force 2020-2030) make catch & release mandatory. Conservation priority; not a salmon fishing destination. The Mawddach holds modest salmon runs but is classified at risk.

Related guides
Yorkshire & SpidersNorth Country methodsEuro Nymphingsubsurface methods
Casting instructors near here
Booking & contacts
Clubs & associations