[denizen467]

^ And it's now a Chicago export too: I remember an article a couple years ago about how cities from around the world send delegations to Chicago to study (or just hire Chicago experts to come and provide services for) the dyeing of rivers. Apparently there's quite a bit of know-how necessary to getting the dye spread out and consistent in a very short period of time. I don't know that it was London or Paris doing it, but I do recall a reference to some mid-sized East European or Russian city and maybe some Chinese cities.