Spate · Slate · North West Wales / Gwynedd, GB-WLS

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.

Prime · Brown Trout
Hare's Ear Nymph · 12-16
Primelive now
About as good as it gets
River high but settled. Coloured water — fish bigger and deeper, confident takes down the seams.
90% confidence
What moved it
  • Level1.52 mLast reading 22h ago
  • Water temp15.1°C
  • ClarityClear
Today's fly
Hare's Ear Nymph
Hare's Ear Nymph12-16
Upstream, sub-surface
Conditions on the water
Live gauge
Level
Steady
1.52 m
Last reading 22h ago
Water temp15.1°C
ClarityClear
Weather17°C
WindSE 11 km/h
Pressure1020 hPa
Rain · recent1.6 mm
Rain · ahead16.7 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
Ideal
15°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
Excellent — water temperature is right today, though time of day could be better.
Likely species
Stoneflies
Caddisflies
Gammarids
Hatch timeline · todayPeak at 11am

Hatch predictions

Today's headline hatch shown — see all 12 active hatches hour by hour as a supporter.

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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 4 as a supporter.

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Evidence
Survey-backed · regionalHigh confidence

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

Through the year
0–3 scale · September 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
March BrownHatch
2
3
2
CapererHatch
2
3
3
2
Heather FlyHatch
2
2
Autumn DunHatch
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
Brown trout · Salmon · Sea trout
Artro
16 km
Brown trout · Salmon · Sea trout
Afon Prysor
17 km
85
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 85 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time60 × 13%7.8
Pressure80 × 7%5.6
Insect activity73 × 12%8.8
Conditions total= 85
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitysurvey-backed invertebrate datasurvey
What would change the calculation
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.

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