Freestone · Limestone · Jura, FR

Héria

Héria terrain map
Marginal · Brown Trout
CDC Emerger · 16-20
New ruleReported 10 Aug 2026

Severe drought restrictions (crise) in force

A préfectoral drought order places this catchment's surface water at crise, the highest of France's four restriction tiers. Fishing itself is not named in the order, but flows are low and water-use restrictions are in force. Zone: Plateau calcaire (dépt 39).

Arrêté préfectoral n°37667

Temporary notices from official orders and recent fishery reports — they clear automatically once out of date.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

Slow going — pick your moments
River lifting fast on the rain. Slow going — pick your moments and do not force it.
45% confidence
limited data
What moved it
  • LevelProxyvia Bienne
  • Water temp17.9°C
  • ClarityVery colouredColouring up
Today's fly
CDC Emerger
CDC Emerger16-20
Dead-drift
Conditions on the water
Proxy gauge
Level
Rising
Proxy
via Bienne
Water temp17.9°C
ClarityVery coloured
Weather19°C
WindSW 15 km/h
Pressure1016 hPa
Rain · recent19.0 mm
Rain · ahead1.6 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
18°C est.ideal 1016°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
Poor — barometric pressure is working for you, but water clarity is the limiting factor today.
Hatch timeline · todayPeak at 6am

Hatch predictions

Today's headline hatch shown — see all 3 active hatches hour by hour with Pro.

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Sub-surface · on the nymphunder the surface

Hatch predictions

See the full sub-surface read with Pro.

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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 · regionalHigh 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
Evening SedgeHatch
2
3
3
3
2
Large Dark OliveHatch
1
2
2
1
Iron BlueHatch
1
2
2
2
2
2
2
1
Blue Winged OliveHatch
1
2
2
2
2
1

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

Ranked for today
Brown Trout fly box
What's coming
Plan ahead
5-day outlook
Fishing better nearby · 5
Water quality (WFD)
  • EcologyGood
  • ChemicalUnknown

WFD classification · FRDR11905

The full read · show the working · for Brown Trout · confidence 45%
How the 30 is built — score × weight = contribution
Temperature44 × 28%12.3
Flow30 × 22%6.6
Clarity15 × 18%2.7
Feeding Time80 × 13%10.4
Pressure80 × 7%5.6
Insect activity52 × 12%6.2
Limiting factor: Water is very coloured — too coloured for Brown Trout= 44
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.
A drop and clear would lift the flow and clarity scores.
Directions
Seasons & zones
  • Trout 2nd Saturday of March3rd Sunday of September
Related guides
Booking & contacts