Freestone · Limestone · Jura

Héria

Héria terrain map

The Héria is classic Jura water on a small scale: a limestone stream with the clarity and temperature stability of a proper chalk river, where the trout live long enough to learn every fly in the box and are perfectly happy to show you they've done so.

Marginal · Brown Trout
CDC Emerger · 16-20
New ruleReported 30 Jul 2026

Severe drought restrictions (crise) in force

The Plateau calcaire zone (Dept 39) 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°37532 ↗

Temporary notices from official orders and recent fishery reports — they clear automatically once out of date.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

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
  • LevelProxyvia Bienne
  • Water temp18.8°C
  • ClarityClear
Today's fly
CDC Emerger
CDC Emerger16-20
Dead-drift
Conditions on the water
Proxy gauge
Level
Steady
Proxy
via Bienne
Water temp18.8°C
ClarityClear
Weather21°C
WindSE 10 km/h
Pressure1015 hPa
Rain · recent0.0 mm
Rain · ahead3.2 mm

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

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 18.8°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 6am

Hatch predictions

Today's headline hatch shown — see all 4 active hatches hour by hour with Pro.

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Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 4 guilds with Pro.

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Beyond the hatch · worth watchingambient prey

Hatch predictions

Top prey shown — see all 2 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
GrannomHatch
2
2
Evening SedgeHatch
2
3
3
3
2
Large Dark OliveHatch
1
2
2
1
Iron BlueHatch
1
2
2
1

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

Ranked for today
Brown Trout fly box

Sight-nymphing and technical dry-fly fishing on very clear trout and grayling rivers, with strong mayfly and sedge windows and highly selective fish.

What's coming
Plan ahead
5-day outlook
Water here around 19°C. Nothing cooler within range — carry a thermometer.
About this water

The Héria is classic Jura water on a small scale: a limestone stream with the clarity and temperature stability of a proper chalk river, where the trout live long enough to learn every fly in the box and are perfectly happy to show you they've done so. The fish are wild, the water is transparent, and the upstream dry-fly drill is the only way to fish it with any self-respect. Work upstream in short, precise casts, keep out of the water when you can, and treat every presentation as if it's your only one. Olives in spring, caddis through June and July, terrestrials in the low water of late summer. This is not a numbers river. It's a river where you go home remembering three fish in detail because each of them required something specific from you.

  • Limestone
Water quality (WFD)
  • Ecology: Good
  • Chemical: Unknown

WFD classification · FRDR11905

The full read · show the working · for Brown Trout · confidence 80%
How the 35 is built — score × weight = contribution
Temperature42 × 28%11.8
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time40 × 13%5.2
Pressure80 × 7%5.6
Insect activity64 × 12%7.7
Conditions total= 65
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowproxy via Bienneproxy
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
Related guides
Pyrenees PlaybookFrench riversEuro Nymphingsubsurface methods
Booking & contacts