This damaging of art and history in the name of climate awareness has been going on for months.....

[ProfessorGAC]

12. A Few Thoughts

We probably disagree on how much attention they're actually drawing to the issue. The coverage of each of these events is dominated by the act itself, not on the reason. I don't think this raises the awareness you suggest.
Now, to the technical aspects. There isn't really any such thing as vegetable charcoal. That's strictly a marketing term. Once the non-carbon constituents have been removed from a complex organic compound, it's literally all the same.
Yes, it's harmless. No, it's not simple to filter.
Elemental carbon capable of dispersing uniformly (and not sinking to the bottom) has to be Mesh 400-800 particle size.
32 - 64 microns. Fountains, like pool filters, are likely to have 200 micron filters, maybe(!) 100.
So, at least 99% of this powder will flow through the in-place filters. In several weeks, we might filter out 50%.
They're going to have to bring in a skid filter with 1 to 5 micron absolute filter socks to clear the water up.
Which leads us to the final piece: they are drawing attention to their cause by making extra work for the average Joe or Jane. Think Joe or Jane care about their cause anymore?