I think the fact the supposed object of protest won't be there is irrelevant, Gary.
As Tom pointed out, that ship's crap is literally a drop in the bucket compared to the waste in out household flushes and fertilizer/runoff.
But, household flushes and runoff are very ubiquitous, making it impossible to swim out to and yell at while in a clown suit.
That makes these sources of pollution horrible candidates for a media event, probably even worse candidates than a ship that doesn't show.