Shame and humiliation are powerful and effective teachers. People should clean up their own messes no matter the scale. When it becomes criminal damage, punishment should be an opportunity for correction and education.
A sign on the work site indicating that the cleanup is being done by the perpetrators may provoke derisive remarks by passersby, but this is part of the correction component. First hand experience of the damage caused by clearing away dead fish and fowl adds an important education element.