Freestone · Sedimentary · Shikoku, JP

Shimanto River

Spring in Shimanto River
Tomorrow · Not the day for it
Sakasa kebari
Forecast · Tomorrow
Not the day for it
Not much stacked in your favour today. Worth an hour if you are nearby, not worth the special trip.
80% projected
Today's fly
Sakasa kebari
Sakasa kebari
Conditions on the water · Tomorrow
Estimate
Level
Light rain recently
No gauge reading
Water temp18.5°C
ClarityClearing
Weather25°C
WindN 11 km/h
Pressure1021 hPa
Rain · recent7.4 mm
Rain · ahead1.3 mm

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

Water temperature for Amago
Warm — slow
19°C est.ideal 9–17°C
0°14°28°
How to fish it · for Amago
When
Spring to the autumn closure (salmonids in the upper river)
Where
The Shimanto is called Japan's last clear river — a long, undammed, gently flowing water through rural Kōchi crossed by its famous low 'sinking bridges',…
Why this works
Water at 18.4°C — above the masu salmon caution line (17°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Hatch timeline · tomorrowPeak at 14h

12h(now) — Heather Fly

Stage: Terrestrials on topApproach: Dry flyActivity: 91%
Also:Glossosoma (Japan)79%Black Gnat59%Isonychia japonica53%
Peak emergence windowWeather boost10 food groups active

Peak activity at 14h — Isonychia japonica (Isonychia japonica, Weather boost)

Sub-surface · on the nymphunder the surface

Hatch predictions

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Beyond the hatch · worth watchingambient prey(1)

Hatch predictions

Top prey shown — see all 3 as a supporter.

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Evidence
Records-basedModerate confidence

Based on species-occurrence records, not local invertebrate surveys.

Through the year
0–3 scale · September highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Stenopsyche CaddisHatch
2
3
3
2
Cicada (Semi)Hatch
2
2
Ephemera strigata (Mid-Reach Keiryu Mayfly)Hatch
2
3
3
3
2
Epeorus latifolium (Riffle Mayfly)Hatch
2
3
3
3
3
3
2

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

Ranked for today
Fly box · Amago
EH
Elk Hair / Stenopsyche caddis
12–14 · Sedge
Evening sedge — twitch or dead-drift it as the light goes.
CB
Cicada & beetle terrestrials (midsummer)
10–12 · Terrestrial
Fish it tight to the bank on warm, breezy days.
Permits & access
Permit required — see local rules.
  • Co-operative yugyoken required; ayu and salmonid rules differ; spawning closure in autumn
  • Confirm the exact reach.
What's coming
Plan ahead
5-day outlook
Water here around 18°C. Nothing cooler within range — carry a thermometer.
Gallery · 2
  1. Spring in Shimanto River
    Japan's longest free-flowing river.
  2. Terrain map of the venue
    Terrain map
Conservation note

White-spotted char (iwana) and amago in the upper reaches (ayu in the lower river).

The full read · show the working · for Amago · confidence 80%
How the 23 is built — score × weight = contribution
Temperature51 × 28%14.3
Flow60 × 22%13.2
Clarity95 × 18%17.1
Feeding Time20 × 13%2.6
Pressure80 × 7%5.6
Insect activity73 × 12%8.8
Conditions total= 62
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 9–17 °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
  • 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