I usually use strike indicators when nymphing rivers, and most of the time I am nymphing on fairly fast and deep waters.
I did have an example of nymphing in very shallow water that was moving fairly fast and this was right up against the shore line drifting a very small nymph over weed beds that were bent over by the flow of the water and were only about 4inchs below the surface.
A few years ago I was on a guided trip on the Missouri River below Craig, Montana. Per normal, there were many, many other people out there, drifting and wading when the water allowed wading. It was rather maddening with so many people and the fishing was 'off', not a lot going on. My guide suggested using a different form of nymphing. He tied on a very small, maybe size 18 or 20 fly, black thread body, thicker black thorax and a white tuff for the gills. He then placed the smallest strike indicator he had, around 1/4 of a inch (you do the conversion for metric ). I guess a 3/8 inch would work. Anyway, this was placed about 12 inches above the fly. No weights. He had me cast right up to the edge of the river and allow the fly/indicator to flow right over the weeds. That is where the larger Browns were hiding and feeding. I spent the better part of the rest of the day fishing that way, when the shoreline allowed it and I caught a lot of nice sized Browns.
Larry ---sagefisher---