Spate · Slate · North West Wales / Gwynedd

Mawddach

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

The Afon Mawddach at Llanelltyd

Jeff Buck - CC BY-SA 2.0

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

Poor · Sea Trout
Black & Silver Tube · 1-2 inch
Poorlive now
Slow going — better windows ahead
River dropping into shape after a lift. Cover the water properly, fish each lie once.
55% confidence
What moved it
  • Level0.16 mDropping after lift
  • Water temp14.8°C
  • ClarityUnfishableColouring up
Today’s fly
BS
Black & Silver Tube1-2 inch
In deep pools and dark water, silhouette and contrast do the work colour cannot. A fly that reads as black against depth is enough. Fish it broadside, hold the swing, let it hang at the dangle — that is when the best fish take.
Conditions on the water
Live gauge
Level
Steady
0.16 m
Dropping after lift
Water temp14.8°C
ClarityUnfishable
Weather15°C
WindS 19 km/h
Pressure1021 hPa
Rain · recent0.0 mm
Rain · ahead8.4 mm

Live readings — water temperature is an estimate where the gauge does not record it.

Water temperature for sea trout
Ideal
15°C est.ideal 8–15°C
0°14°28°
How to fish it · for sea trout
When
June through September; July into August prime. Night fishing from full dark when water rises above 13°C. NRW classifies the sewin stock 'At Risk' across Wales — fish carefully if at all, treat C&R as a default. Fast 3-hour response means windows after rain are brief — book the river loosely and fish when it shapes up.
Where
Lower Mawddach pool tails through to the Barmouth tidal limit.
Method
Across-and-down on a floating line with small wets — Medicine, Teal Blue and Silver, Stoat's Tail. Steady swing through the tail-outs, never hurry.
Kit
10 ft #6/7, floating line, 8 to 10 lb fluoro tippet. Spare leader on a wrist spool. Headlamp sparingly; let your eyes adjust.
Why this works
Poor — water temperature is working for you, but water clarity is the limiting factor today. ⏰ Sea trout become most active from an hour before dusk. This stretch closes at 21:35 — your legal window captures the start of the best fishing. Fish the last 90 minutes hard. Overcast evenings extend the effective window. ⏰ Sea trout become most active from an hour before dusk. This stretch closes at 21:34 — your legal window captures the start of the best fishing. Fish the last 90 minutes hard. Overcast evenings extend the effective window.
Hatch timeline · todayQuiet day

Hatch predictions

Today's headline hatch shown — see all 4 active hatches hour by hour with Pro.

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Evidence
Survey-backed · regionalModerate confidence

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

Through the year
0–3 scale · July 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
Sea Trout fly box
BS
Black & Silver TubeTop
1-2 inch · Tube
In deep pools and dark water, silhouette and contrast do the work colour cannot. A fly that reads as black against depth is enough. Fish it broadside, hold the swing, let it hang at the dangle — that is when the best fish take.
SF
Snake Fly (Black)
2-4 inch · Streamer
A mobile eel-like profile that undulates through deep pools — effective when sea trout are lying deep and not responding to conventional wets.
What's coming
Plan ahead
5-day outlook
Fishing better nearby · 5
Dovey (Dyfi)
18 km
64
Brown trout · Salmon · Sea trout
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
Brown 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.

  • 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 sea trout · confidence 55%
How the river scores — hydrology factors
Water heightMedium Ideal0.0
Recent riseNone0.0
Falling after liftNot Applicable0.0
Water temperatureCool To Moderate0.0
Time in seasonOpening Period0.0
ClarityClearing0.0
Hydrology base0.0
Legal gate: Unknown Check Local Rules
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Salmon20 March → 17 October
  • Trout3 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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