Karst · Limestone · Jura / Doubs

Cusancin

A small clear river flowing over a low weir, lined with autumn trees, in the Cusancin valley, France.
Poor · Brown Trout
CDC Emerger · 16-20
New ruleReported 17 Jul 2026

Severe drought restrictions (crise) in force

The Plateau calcaire jurassien zone (Dept 25) is at crise — the second-highest French drought tier — under a préfectoral arrêté. Fishing itself is not named as prohibited, but water is severely restricted and flows are likely very low; fish with care and check locally.

Arrêté préfectoral n°37370 ↗

Temporary notices from official orders and recent fishery reports — they clear automatically once out of date.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

Poorlive now
Not the day for it
River temperature is the limiting factor today, not the flow. This is not the day to push it. Check the thermal advice above before you head out.
90% confidence
What moved it
  • Level0.14 mLast reading 2h ago
  • Water temp22.9°C
  • ClarityClear
Today's fly
CDC Emerger
CDC Emerger16-20
Dead-drift
Conditions on the water
Live gauge
Level
Steady
0.14 m
Last reading 2h ago
Water temp22.9°C
ClarityClear
Weather34°C
WindW 10 km/h
Pressure1016 hPa
Rain · recent0.0 mm
Rain · ahead3.8 mm

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

Water temperature for Brown Trout
Warm — slow
23°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Through the open trout season. The Cusancin is small intimate karst water — read each lie carefully. Spring olives, summer sedges, autumn small flies.
Where
Pool tails, weeded glides, the cushion behind chalk boulders. The Cusancin is short and small-scale — short casts, careful approach.
Method
Upstream dry to spotted rising fish; long fine leader. The water reads clear — careful approach matters more than fly choice. Move slowly upstream, cast accurately, accept the result.
Kit
9 ft #4 — French karst-stream default. Floating line, 14 ft leader to 4 lb fluoro. Polarising glasses non-negotiable.
Why this works
Water at 22.9°C. This is the line where catch-and-release kills brown trout. Do not fish for them today.
Hatch timeline · todayPeak at 6pm

Hatch predictions

Today's headline hatch shown — see all 9 active hatches hour by hour with Pro.

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Beyond the hatch · worth watchingambient prey

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 · 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
1
Brown SedgeHatch
2
3
2
Freshwater ShrimpHatch
2
3
3
3
3
3
3
3
3
3
3
2
Blue Winged OliveHatch
2
3
3
3
3
2
Mayfly (Green Drake)Hatch
2
2

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

Ranked for today
Brown Trout fly box
Permits & access
Permit required — see local rules.
  • Permis AAPPMA obligatoire
  • Certains parcours sont privés ; parcours mouche seule et no-kill sur une partie de la rivière
  • Quotas réduits et cannes courtes recommandés.
What's coming
Plan ahead
5-day outlook
Water here around 23°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
  1. A small clear river flowing over a low weir, lined with autumn trees, in the Cusancin valley, France.
    cusancin
  2. Terrain map of the venue
    Terrain map
Water quality (WFD)
  • Ecology: Moderate
  • Chemical: Unknown
What this classification means

WFD ecological status Good → Moderate corrected to EEA WISE 2022 (3rd RBMP) classification for waterbody FRDR11271 (was a stale earlier-cycle value). Source: EEA WISE SWB_SurfaceWaterBody (discodata.eea.europa.eu), verified 2026-06-18.

WFD classification · FRDR11271

The full read · show the working · for Brown Trout · confidence 90%
How the 4 is built — score × weight = contribution
Temperature2 × 28%0.6
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time65 × 13%8.5
Pressure80 × 7%5.6
Insect activity59 × 12%7.1
Limiting factor: Water temperature (22.9°C) is outside Brown Trout's preferred range (10–16°C)= 57
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
  • Trout 2nd Saturday of March → 3rd Sunday of September
  • Grayling 3rd Saturday of May → 3rd Sunday of September

    France national rule: grayling opens 3rd Saturday of May in all waters. In 1st category (salmonid) rivers, grayling closes with the trout season on the 3rd Sunday of September. Departmental regulations may impose additional restrictions. Always check the relevant département's 2026 arrêté préfectoral.

Related guides
Grayling Playbookgrayling tacticsPyrenees PlaybookFrench riversEuro Nymphingsubsurface methods
Booking & contacts