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.

Tomorrow · Closed season
Hare's Ear Nymph
Forecast · Tomorrow
Closed season
Out of season. File this water for the right month.
45% projected
Today's fly
Hare's Ear Nymph
Hare's Ear Nymph
Conditions on the water · Tomorrow
Live gauge
Level
Rising
0.19 m
Lifting fast
Water temp7.4°C
ClarityUnfishable
Weather4°C
WindN 19 km/h
Pressure1013 hPa
Rain · recent5.5 mm
Rain · ahead9.9 mm

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

Water temperature for Sea Trout
Cool — slow
7°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.
Likely species
Stoneflies
Gammarids
Hatch timeline · tomorrowPeak at 11am

12pm(now) — Autumn Needle Fly

Stage: Creeping nymphsApproach: Heavy nymphActivity: 36%
Peak emergence window

Peak activity at 11am — Autumn Needle Fly (Autumn Needle Fly, Peak emergence window)

Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 3 guilds as a supporter.

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

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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 · November 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
Sea 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.

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.
Medicine Fly
Medicine Fly
8–12 · Streamer
Slim and mobile — fished sunk through the pool when surface work is not producing. Consistently takes fish that will not come to the surface.
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
Dysynni
14 km
0
Brown trout · Salmon · Sea trout
Artro
16 km
0
Brown trout · Salmon · Sea trout
Dovey (Dyfi)
18 km
0
Brown trout · Salmon · Sea trout
Afon Eden (Welsh)
5.0 km
Brown 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

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 Sea Trout · confidence 75%
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
  • 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
Boards & regulators
At a glance

Mawddach is a spate river in North West Wales / Gwynedd. The catchment geology is recorded as slate, and the water sits at about 21 m above sea level. The river is described as roughly 28 km long. Species listed for this water: brown trout, salmon and sea trout. It is classed as a salmon river. The salmon season is recorded as running from 20 March to 17 October. The trout season is recorded as running from 3 March to 30 September. Best window recorded for anglers: May to September. Core methods listed: upstream nymph; dry fly; small wet fly. Level and flow data for this water is linked from 2 gauges. Its Water Framework Directive ecological status is recorded as moderate. Nearby waters in our listings include Afon Eden (Welsh) at 5.0 km, Dysynni at 14 km and Artro at 16 km.