Lean, green, dye-ing machine

Because most likely it's 100% safe food coloring dye or something similar that wouldn't cause issues for the local fauna

The dye poured into the river for St. Patrick's is non-pollutant. They've been doing it since 1962, and no issues have cropped up. Supposedly the recipe for the stuff is a closely guarded secret. It starts as an orange dye before it turns the river green. The only worry from enviros is that copycats might start dying rivers with non-safe materials.