I could add that the fishies are brown trout.
Some people do good fishing with worms downstream, at least 10 meters ahead they say, so why not flies.

Those streamers then may not sink.

Yes this is an interesting challenge, I have not fished it that many times, it's a river that flows into my favorite lake.
But I find my self often thinking of how to tackle this nice "problem".

Thank you both for your answers.

Reg,
Thorarinn