Mountain Freestone · Granite · Honshū

Itoshiro River

Mount Choshi and Itoshiro River
Marginal · Rainbow Trout
Cicada (foam semi pattern) · 6-10
Marginallive now
Slow going — pick your moments
Low and clear — careful approach country. Cover and shadow are doing the work today.
90% confidence
What moved it
  • LevelLight rain recentlyNo gauge reading
  • Water temp18.2°C
  • ClarityClear
Today's fly
CI
Cicada (foam semi pattern)6-10
High-confidence seasonal pick
Conditions on the water
Estimate
Level
Light rain recently
No gauge reading
Water temp18.2°C
ClarityClear
Weather16°C
WindNE 4 km/h
Pressure1009 hPa
Rain · recent2.7 mm
Rain · ahead10.2 mm

No gauge on this water — readings are regional estimates from weather, not a live gauge.

Water temperature for Rainbow Trout
Warm — slow
18°C est.ideal 10–18°C
0°14°28°
How to fish it · for Rainbow 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 18.2°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

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Sub-surface · on the nymphunder the surface

Hatch predictions

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Beyond the hatch · worth watchingambient prey

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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
Stenopsyche CaddisHatch
2
3
3
2
Cicada (Semi)Hatch
2
2
Large Dark OliveHatch
1
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
Rainbow Trout fly box
Permits & access
Permit required — see local rules.
  • Local fishery co-operative yugyoken required; spawning closure around 30 September
  • Confirm exact reach and method rules.
What's coming
Plan ahead
5-day outlook
Water here around 18°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
  1. Mount Choshi and Itoshiro River
    Alpine river with mountain backdrop.
  2. Terrain map of the venue
    Terrain map
Conservation note

White-spotted char (iwana) and amago — the Pacific-side red-spotted masu trout — with some stocked rainbow.

The full read · show the working · for Rainbow Trout · confidence 90%
How the 39 is built — score × weight = contribution
Temperature93 × 28%26.0
Flow80 × 22%17.6
Clarity85 × 18%15.3
Feeding Time85 × 13%11.1
Pressure75 × 7%5.3
Insect activity67 × 12%8.0
Conditions total= 83
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Char late February to April → late September to mid-October

    Honshu/Shikoku/Kyushu keiryu are managed by local fishery co-operatives — a yugyoken (day/annual ticket) is required, and most streams close around 30 September / mid-October for spawning. Species are surfaced in prose only (no engine slugs for yamame, amago or iwana). Legal status: guidance_not_permission.

Related guides
Euro Nymphingsubsurface methods
Booking & contacts