What are those leprechauns using if not fluorescein?

I posted Sunday and last year about the putative use of fluoresciein in the Chicago river on St. Patrick's day. As some readers pointed out, they apparently aren't using it anymore.

I don't even have a guess what they're using, then. The reason the solid dye is orange is because it absorbs blue-green light, and the reason the river looks green is because it fluoresces, emitting green-green light.

Whatever they're dumping in the river has about that absorption spectrum and about that emission spectrum, and it's got to have a very high emission quantum yield (that is, it has to convert absorbed bluish-green light into emitted green light efficiently). Fluorescein does this with 97% efficiency.

What they're using looks very much like fluorescein. The emitted light looks pretty close to that of fluorescein. That's the wavelength range your eyes are best at, and that's the distinctive Ecto Cooler green color your green laser pointer puts out.

Any guesses? I am not entirely convinced they're using something other than fluorescein. It's cheap, and it's not that nasty; it's used (in much smaller quantities) as a tracer for pipes leaking into groundwater.

Oh, and on another note, fluorescein is what makes antifreeze green (not why it's so toxic, though).