After several unsuccesfull tries with the dry fly I took time to observe the rings and the way the fish took
They were "nymphing" just under the surface and not bothering the many winged drifting insects.
I changed my dry fly with an unweighted small dark nymph. I repeated the upstream cast and
let the nymph drift with the current, exactly where I had seen a fish rasing a few seconds earlier, the fish took the
nynph at once and after realising the deception jumped out of the water to then try to gain the faster current.
It turned out to be a nice rainbow of about 1 kilo.