Spring Fed · Karst · Lika-Senj / Otočac, HR

Gacka

Photo of Gacka

Croatia's flagship trout river — a classic karst spring creek rising fully formed from limestone near Otočac.

Tomorrow · A proper day on the water
Czech Nymph
Forecast · Tomorrow
A proper day on the water
A proper day for it. Work the seams with an upstream nymph, switch to the dry when they show.
65% projected
Today's fly
Czech Nymph
Czech Nymph
Conditions on the water · Tomorrow
Live gauge
Level
Rising
1.66 m
Lifting fast
Water temp9.3°C
ClarityVery coloured
Weather5°C
WindN 7 km/h
Pressure1019 hPa
Rain · recent45.6 mm
Rain · ahead15.7 mm

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

Water temperature for Grayling
Ideal
9°C est.ideal 4–14°C
0°14°28°
How to fish it · for Grayling
When
Midday window — grayling feed best from late morning into early afternoon.
Where
Work runs and glides — grayling shoal in the bottom third of the water column.
Method
Tight-line nymph the bottom third with weighted patterns.
Kit
10 ft #3 rod, floating line, long leader to 4 lb fluoro for nymphs.
Why this works
Good — water temperature is right today, though water clarity could be better. Grayling feeds actively in cold water — peak winter sport.
Likely species
Gammarids
Hatch timeline · tomorrowPeak at 12pm

12pm(now) — Autumn Olive

Stage: On emergersApproach: Emerger or dryActivity: 33%
Peak emergence window4 food groups active

Peak activity at 12pm — Autumn Olive (Autumn Olive, 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

Top prey shown — see all 2 as a supporter.

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Evidence
Records-basedModerate confidence

Based on species-occurrence records, not local invertebrate surveys.

Through the year
0–3 scale · November highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
1
2
2
2
2
2
2
1
Grayling seasonSeason
1
2
2
2
2
2
2
1
Freshwater ShrimpHatch
2
3
3
3
3
3
3
3
3
3
3
2
Brown SedgeHatch
2
3
3
3
2
Small SpurwingHatch
2
3
3
3
2
Small Dark OliveHatch
2
3
3
3
2

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

Ranked for today
Grayling fly box

Ultra-clear spring-fed rivers with large educated trout. Sight fishing, technical presentation, fine tippets. Euro-nymphing dominant subsurface method. Exceptional dry-fly windows during hatch periods. Gacka is the flagship water.

Small Perdigón
Small Perdigón
Hook 14–18 · Fly
in season
Permits & access
Permit required — see local rules.
  • Croatian fishing licence required
  • Local concessionaire permit needed
  • Zone A is fly-only catch-and-release; wider Gacka rules vary by zone, so fish the named zone rather than the river name alone.
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Mrežnica
40 km
79
Brown trout · Grayling
Dobra
46 km
86
Brown trout · Grayling
Vitunjčica
47 km
Brown trout
Korana
48 km
Brown trout
Una
50 km
0
Brown trout · Grayling · Hucho
Gallery · 2
  1. Photo of Gacka
    Gacka
  2. Terrain map of the venue
    Terrain map
About this water

Crystal-clear, slow-moving water with large wild brown trout in weed beds and undercuts. The main course is managed through Zones A, B and C, with a separate Zone D lake/grayling area in the wider fishery structure. Spring-fed character gives constant temperature and gin-clear water year-round — extending the season well into summer when freestone rivers struggle. Technical dry fly and sight nymphing in true chalk-stream conditions. One of the few genuine spring creek ecosystems in Southern Europe. WFD ecological status is 'Moderate' — likely reflecting nutrient inputs or modified hydrology rather than poor fishing quality; the managed fly zones remain productive.

  • Karst
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown

WFD classification · HRJKRN0269_001

The full read · show the working · for Grayling · confidence 65%
How the 72 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow55 × 22%12.1
Clarity45 × 18%8.1
Feeding Time90 × 13%11.7
Pressure80 × 7%5.6
Insect activity58 × 12%7.0
Conditions total= 73
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout 1 March → 31 October
  • Grayling 15 May → 31 December

    Gacka is an iconic Croatian spring-creek fishery — catch-and-release only for both grayling and brown trout along the entire river. Retention of grayling is prohibited. Fishing downstream of the zero bridge is allowed subject to concession rules. One rod, artificial fly or lure only. Check current concession holder rules — the Gacka is a conservation-priority water.

    All grayling must be returned — retention is prohibited here.

Related guides
Chalkstream Playbookkarst spring river — same tacticsGrayling Playbookgrayling tacticsEuro Nymphingsubsurface methods
Booking & contacts
At a glance

Gacka is a river in Lika-Senj / Otočac, Croatia. The catchment geology is recorded as karst, and the water sits at about 451 m above sea level. Species listed for this water: brown trout and grayling. The trout season is recorded as running from 1 March to 31 October. The grayling season is recorded as running from 15 May to 31 December. Core methods listed: Dry fly; Upstream nymph; Small wet. Level and flow data for this water is linked from 1 gauge. Its Water Framework Directive ecological status is recorded as moderate. Nearby waters in our listings include Mrežnica at 40 km, Dobra at 46 km and Vitunjčica at 47 km.