Spate · Slate Shale Snowdonia · Wales / Snowdonia (Trawsfynydd), GB-WLS

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.

Today · Not the day for it
Partridge and Orange
Forecast · Today
Not the day for it
Not much stacked in your favour today. Worth an hour if you are nearby, not worth the special trip.
45% projected
Today's fly
Partridge and Orange
Partridge and Orange
Conditions on the water · Today
Proxy gauge
Level
Rising
Proxy
via Conwy
Water temp13.0°C
ClarityUnfishable
Weather15°C
WindN 23 km/h
Pressure1014 hPa
Rain · recent4.6 mm
Rain · ahead26.4 mm

No gauge on this water — conditions are inferred from Conwy. The trend transfers, the absolute level does not.

Water temperature for Brown Trout
Ideal
13°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 19.8°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 12pm

12pm(now) — Heather Fly

Stage: Terrestrials on topApproach: Dry flyActivity: 63%
Also:Daddy Long Legs62%Autumn Dun33%Autumn Needle Fly24%
Peak emergence window11 food groups active

Peak activity at 12pm — Heather Fly (Heather Fly, Peak emergence window)

Sub-surface · on the nymphunder the surface

Hatch predictions

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 3 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 · September highlighted
J
F
M
A
M
J
J
A
S
O
N
D
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

Spider-heavy and practical. Strong tradition of North Country soft hackles, useful nymphing, and simple dry flies when fish rise properly.

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.
Visit official site ↗
What's coming
Plan ahead
5-day outlook
Water here around 20°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 28 is built — score × weight = contribution
Temperature14 × 28%3.9
Flow80 × 22%17.6
Clarity40 × 18%7.2
Feeding Time85 × 13%11.1
Pressure80 × 7%5.6
Insect activity51 × 12%6.1
Limiting factor: Water temperature (19.8°C) is outside Brown Trout's preferred range (10–16°C)= 52
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowproxy via Conwyproxy
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.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 3 March → 30 September
Related guides
Yorkshire & SpidersNorth Country methodsEuro Nymphingsubsurface methods
Casting instructors near here
Booking & contacts
Clubs & associations