Mountain Freestone · Granite · Honshū

Itoshiro River

Mount Choshi and Itoshiro River
Poor · Rainbow Trout
Cicada (foam semi pattern) · 6-10
Poorlive now
Not the day for it
Low and clear — careful approach country. A morning for the obvious fish only.
90% confidence
What moved it
  • LevelDry recentlyNo gauge reading
  • Water temp22.0°C
  • ClarityClear
Today's fly
CI
Cicada (foam semi pattern)6-10
High-confidence seasonal pick
Conditions on the water
Estimate
Level
Dry recently
No gauge reading
Water temp22.0°C
ClarityClear
Weather24°C
WindNW 15 km/h
Pressure1006 hPa
Rain · recent0.0 mm
Rain · ahead8.9 mm

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

Water temperature for Rainbow Trout
Warm — slow
22°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 22°C. This is the line where catch-and-release kills brown trout. Do not fish for them today.
Likely species
Mayflies
  • Blue-winged oliveMost likely
    #16–18 · Dun
    Duns are up; a sherry spinner fall may follow.
  • Large dark oliveAlso possible
    #14–16 · Emerger
    Dead-drift the emerger — it's sitting in the film.
  • Green drakeAlso possible
    #8–10 · Spinner
    Spinners on the water now — the big fish move for these.
  • Iron blue mayflyAlso possible
    #16–18 · Dun
    Cold, grey day — the dun sits long. Good dry-fly water.
Caddisflies
  • Satin sedgeMost likely
    #12–14 · Egg-laying
    Skitter it at dusk — this one's fished, not dead-drifted.
  • GrannomAlso possible
    #14–16 · Pupa
    Pupa first, then dries as the adults come off.
Hatch timeline · todayPeak at 6pm

Hatch predictions

Today's headline hatch shown — see all 2 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
ModelledModerate confidence

Modelled from regional ecology — no survey or occurrence data for this water yet.

Updated 6 hours ago

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 22°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 15 is built — score × weight = contribution
Temperature11 × 28%3.1
Flow60 × 22%13.2
Clarity85 × 18%15.3
Feeding Time80 × 13%10.4
Pressure75 × 7%5.3
Insect activity57 × 12%6.8
Limiting factor: Water temperature (22°C) is outside Rainbow Trout's preferred range (10–18°C)= 54
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
What would change the calculation
Cooler water — back toward the 10–18 °C ideal band — would lift the score and ease welfare.
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