Not so sure about the reason given in the link above. First off what would be the reason to engage in such a prank? Also the amount of dye necessary to turn a entire river green like that would be huge in quantity...who has this much money to waste on such a "prank"? It should be easy to find the culprits as buying this quantity of a dye this color should easily set off bells to the distributor of the dye as to who bought it? Also few and far between are the products...especially dyes, that are HARMLESS as the article claims. This is a LOT OF DYE in this river, which the article never says what the constituents of the dye are made of (most are from NON ORGANIC sources that DON'T break down easily and do have an effect). A little bit of the dyes used on easter eggs, food and clothing may not be bad, but this quantity?... I would be worried about...especially since the "culprits" have not been identified...maybe it was Osama or Muqtada or KSM..I am sure those names will rise eventuially.
Maybe it was a bad batch of purple food colouring that the dumped... and with a little e coli or raw sewage... voila... bright flourescent neon green.