Freestone · Limestone · Primorska / Idrija

Cerknica (Idrijca tributary)

Cerknica (Idrijca tributary) terrain map
Prime · Marble Trout
Blue-Winged Olive · 18-20
Temporary closure · troutReported 31 Jul 2026

Total fishing suspension in force (low water / high temperature)

RD Idrija had a total suspension of fishing in force as of 31 July 2026 for low water and high water temperature, alongside a national low-water welfare warning live on ribiskekarte.si. This is a biophysical do-not-fish state, not a routine seasonal closure — check RD Idrija's current notice before travelling.

RD Idrija club announcements ↗

Temporary notices from official orders and recent fishery reports — they clear automatically once out of date. Always confirm locally before travelling.

Primelive now
About as good as it gets
River high but settled. Coloured water — fish bigger and deeper, confident takes down the seams.
80% confidence
What moved it
  • LevelProxyvia Idrijca
  • Water temp11.1°C
  • ClarityClearingClearing
Today's fly
Blue-Winged Olive
Blue-Winged Olive18-20
Upstream dry, on top
Conditions on the water
Proxy gauge
Level
Falling
Proxy
via Idrijca
Water temp11.1°C
ClarityClearing
Weather20°C
WindNE 6 km/h
Pressure1019 hPa
Rain · recent0.0 mm
Rain · ahead0.0 mm

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

Water temperature for Marble Trout
Ideal
11°C est.ideal 8–13°C
0°14°28°
How to fish it · for Marble 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
Excellent — water temperature is right today, though insect activity could be better.
Likely species
Mayflies
  • Iron BlueMost likely
    #16–18 · Dun
    Cold, grey day — the dun sits long. Good dry-fly water.
  • Large dark oliveAlso possible
    #14–16 · Emerger
    Dead-drift the emerger — it's sitting in the film.
  • Blue-winged oliveAlso possible
    #16–18 · Dun
    Duns are up; a sherry spinner fall may follow.
Caddisflies
  • GrannomMost likely
    #14–16 · Pupa
    Pupa first, then dries as the adults come off.
  • Net-spinning caddis (S. Europe)Also possibleLower confidence
    #12–14–16 · Pupa
    Widespread riffle net-spinner; evening emergence.
Hatch timeline · todayQuiet day

Hatch predictions

Today's headline hatch shown — see all 7 active hatches hour by hour with Pro.

Start free trial

14-day free trial. Cancel anytime.

Sub-surface · on the nymphunder the surface

Hatch predictions

See the full sub-surface read with Pro.

Start free trial

14-day free trial. Cancel anytime.

Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 3 with Pro.

Start free trial

14-day free trial. Cancel anytime.

Evidence
ModelledModerate confidence

Modelled from regional ecology — no survey or occurrence data for this water yet.

Through the year
0–3 scale · August highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
1
Grayling seasonSeason
1
2
2
2
2
2
1
GrannomHatch
2
2
Evening SedgeHatch
2
3
3
3
2
Alpine RhithrogenaHatch
1
2
2
1
Large Dark OliveHatch
1
2
2
1

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Marble Trout fly box
Permits & access
Permit required — see local rules.
  • RD Idrija, District B
  • Mandatory C&R, fly-only, barbless.
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Kanomljica
2.0 km
Marble trout · Marble brown hybrid trout · Brown trout
Idrijca
8.0 km
Brown trout · Marble trout · Grayling
Hubelj
17 km
30
Marble trout · Marble brown hybrid trout · Brown trout
Kneža
17 km
Marble trout · Brown trout · Grayling
Poljanska Sora
18 km
Grayling · Brown trout · Rainbow trout
The full read · show the working · for Marble Trout · confidence 80%
How the 84 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow85 × 22%18.7
Clarity75 × 18%13.5
Feeding Time85 × 13%11.1
Pressure80 × 7%5.6
Insect activity56 × 12%6.7
Conditions total= 84
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowproxy via Idrijcaproxy
Prey activitymodelled from regional profilemodelled
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 1 March → 30 September
  • Grayling 16 May → 30 November

    Slovenian common default: grayling 16 May – 30 November (lipan). Permit and fishing district controlled — dates may vary by specific water. Always check the Ribiška Družina (fishing district) permit for the specific beat.

    Prime sport 1 September → 30 November

  • Marble trout 1 April → 31 October
Related guides
Grayling Playbookgrayling tacticsAlpine Streamsmountain entomologyMarble TroutSoča system
Booking & contacts