Spate · Slate Shale Snowdonia · Wales / Snowdonia (Trawsfynydd)

Afon Prysor

The Afon Prysor, a Welsh upland stream, flowing near Trawsfynydd in Gwynedd

Prysor is a small Snowdonia spate river above Trawsfynydd Lake — narrow water with a good head of wild brown trout to a pound and a half, two short Passport beats, mostly double bank.

Marginal · Brown Trout
Pheasant Tail Nymph · 14-16
Marginallive now
Slow going — pick your moments
River temperature is the limiting factor today, not the flow. Fish dawn or dusk if you go at all, and handle everything with extra care.
80% confidence
What moved it
  • LevelDry recentlyNo gauge reading
  • Water temp19.4°C
  • ClarityClear
Today's fly
Pheasant Tail Nymph
Pheasant Tail Nymph14-16
Upstream, sub-surface
Conditions on the water
Estimate
Level
Dry recently
No gauge reading
Water temp19.4°C
ClarityClear
Weather19°C
WindN 16 km/h
Pressure1021 hPa
Rain · recent0.0 mm
Rain · ahead0.4 mm

No gauge on this water — readings are regional estimates from weather, not a live gauge.

Water temperature for Brown Trout
Warm — slow
19°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Nymphing can work through most of the day.
Where
Cover mixed depths.
Method
Start with tight-line nymphs and adjust if fish rise or drift higher.
Kit
9 ft #4 rod, floating line, 12 ft tapered leader to 4–5 lb fluoro tippet.
Why this works
Water at 19.4°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · todayPeak at 6pm

Hatch predictions

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Sub-surface · on the nymphunder the surface

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Beyond the hatch · worth watchingambient prey

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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 · July highlighted
J
F
M
A
M
J
J
A
S
O
N
D
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
Beats · 1
Afon Prysor — Beats 1 & 2 via Fishing PassportAccess varies
Two short day-ticket beats on the Prysor above Trawsfynydd — Beat 1 (1 mile, double bank) and Beat 2 (1½ miles, double bank), £10/day each.
What's coming
Plan ahead
5-day outlook
Water here around 19°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
  1. The Afon Prysor, a Welsh upland stream, flowing near Trawsfynydd in Gwynedd
    Afon Prysor upstream of Pont Trawsfynydd, Gwynedd
  2. Terrain map of the venue
    Terrain map
About this water

Prysor is a small Snowdonia spate river above Trawsfynydd Lake — narrow water with a good head of wild brown trout to a pound and a half, two short Passport beats, mostly double bank. Properly small fishing on rocks and pockets; six-foot rod, dry-dropper, and a willingness to fish slowly. The kind of river you fish on the way somewhere else and remember after.

  • Slate shale snowdonia
The full read · show the working · for Brown Trout · confidence 80%
How the 31 is built — score × weight = contribution
Temperature33 × 28%9.2
Flow60 × 22%13.2
Clarity95 × 18%17.1
Feeding Time65 × 13%8.5
Pressure80 × 7%5.6
Insect activity57 × 12%6.8
Conditions total= 60
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
  • Trout3 March → 30 September
Related guides
Yorkshire & SpidersNorth Country methodsEuro Nymphingsubsurface methods
Booking & contacts