I hadn’t thought of a boat barricade like that. It would definitely be effective in the short term. Unfortunately, in the US at least, the coast guard would end it real quick for national security reasons. That would certainly make international news though.
I would say protesting at a port would be less likely to garner international attention, and probably would be easier to shutdown quickly and relatively quietly.
Shutting down an airport is much more public, therefore probably safer in the long run. Also more likely to be reported on because it affects the public in a more direct way. Yes, it inconveniences some people, but it gets the message out.
Either way, I doubt it will do much to change anything soon enough.
They use this mixture at my work as well. Flushing out large sub freezing cooling systems. We don’t dump it out on the street though.