Being a diatom, it doesn't favor acidic water, and that one prefers water without much nutrient load in general, especially the warmer and slower eddies of otherwise cold, clear rivers or small lakes. It would probably flourish if you boosted the nitrogen or phosphorus a little bit in some place it was already growing, but it isn't found in eutrophic settings AFAIK.
People only study those kinds of things when they cause problems - other than making fly fishermen slip on rocks in the northwestern US, I don't recall hearing of any problems with the stuff. You trying to grow it in an aquarium?
It certainly doesn't require fertilization to flourish - it's been years since I was familiar, but IIRC it was one of our marker species for cold, low-nutrient (and higher pH, of course) water.
I wouldn't guess, as a first assumption, that its mere presence was a consequence of effluent fertilization from a sewage treatment plant, in other words. Where are you?
Any sources of silica in the effluent?
I think I meant silicates, which are quite different from silica (it's been a while). But higher silicate levels could explain the increased diatom presence in the downstream waters, since they use it for their shell-like structures.