For World Water Day, Greenpeace created an interactive guerilla campaign to bring awareness about fashion brands polluting our rivers & water sources. To entice the audience, a billboard covered with non-toxic ink asks the question “Want to know a dirty little secret?” The answer can be uncovered when the billboard is washed down with water. This campaign is in conjunction with Greenpeace’s detox campaign, in which major fashion brands are challenged to ‘detox’ their manufacturing to prevent poisoning waterways.

Watch how the billboards work:

[via]