Mountain Streams in Japan 1: Fundamental

2012/1/22 Mountain Streams in Japan 1: Fundamental

This part of my tips mostly cover situations in mountain streams in Eastern Japan which is probably the same throughout this main island of Honshu. I have created this article sometimes ago to help traveling angler to Japan.

A. Nature of Mountain Streams in Eastern Japan

On the main island, mountains near metropolitan area have suffered generations of environmental challenges and the height came during the WWII when broadleaf forest vanished due to excessive demand of fire wood. After the war, government re-planted mountains into conifer forest whose soil does not hold as much rainwater or microbiology as broadleaf forest’s.

Without having proper balance or life cycle, rivers don’t have right mix of nutrients to support prosperous ecosystem. Therefore, aquatic and terrestrial insects are usually smaller and fewer. Thus fish feeding on insects don’t grow too big.

This is not so true as you travel to less populated northern Japan where plenty of broadleaf forest are preserved to nurture rich ecosystem. Yet, they share the next issue: dam. Most rivers are segmented by countless small dams from estuary all the way to head water.

This is why population of fish does not grow too big either and why we keep stocking waters throughout the main island.

B. Nature of Native Fish in Mountain Streams

Second consideration is how rivers flow. Japanese mountain streams consist of series of short & fast runs with gin clear water surrounded by short height vegetation casting complex light/shadow on surface. This trains fish into good hunters to identify what’s edible. Native species such as chars and land-locked salmons are accustomed to this over generations, so they can stay in fast water while being able to stay careful on selective feeding.

Imported species such as rainbow trout and brown trout aren’t as susceptive, but then they learn to stay in slower water to match their style.

It’s all survival instinct so that they don’t feed on drifting debris which don’t give them enough nutrition. They do make mistake, and that’s the chance we are fly fishing for.

C. Selection of Fly

So, the choice of fly aren’t so much of imitation, but impression of distinctive shape, size, and how high or low they position to surface.

My usual selections are:

Type                 size                       insect and stage

Midge:         #30-22           Adult, emerger/pupa, larvae

Mayfly:         #18-12           Nymph, emerger, dun, spent

Caddis:         #18-12           Cased nymph, emerger, floating pupa, dun

Stonefly:       #14-10          Nymph only

Terrestrial:    #14-10         Ants, crickets, and beetles


As for colour, you need both pale and dark versions to make your fly stand out in variety of light condition. Use dark for low light condition or in cold day when insects hatch in darker colours. Pale for high light condition or in warm day when insects hatch in paler colours.  Never white. White reflects lays of light too unnaturally which fish can tell.

Presentation requires good natural drift to mimic real situation, more likely so for native species or pressured waters. Next section will cover how it goes in action.