That is the most informative info I have ever read about didymo, thanx for posting SS, as goes a long way towards explaining some of the puzzling aspects connected to the spread of such a horrible invasive scourge.Sorry, Hi-jack... Rock snot.
We can SLOW spreading of invasive species but it will not be stopped, at least not in my lifetime. People are mobile. Some are ignorant, don't think, are lazy or don't care.
Even tho it is still only an unproven finding, it could provide an answer to why it can move upstream (albeit slower than down river) also why a certain river can be affected yet another that joins it is not.
One aspect of the report I find at odds with tho is the description (quote)
Seemingly out of nowhere mucus-like, thick gelatinous mats of yellowish -brown algae were found clinging to rocks on the river bottoms. (unquote)
That would be a good description of the stuff down here in appearance, but to the touch has a deceptively coarse feel to it more like sandpaper or shark skin.