100,000 LED Spheres Floating Down a River in Japan

Would have been more exciting to drop 100,000 dollar bills from a helicopter....

? in Japan ... they would have drop it (the entire pack) on to someones head ... so they'd have later to bow for the lost ones memory (be aware of what you suggest!)

Did somebody retrieve them after the event?

Why on earth would one do that?

from the article:

After illuminating a large stretch of the river, which also hosts a popular fireworks festival in the summer, the LEDs were all caught in a large net.

I count only 98,734 LED spheres.

Using LEDs/batteries inside plastic spheres was a patently stupid way to implement these, quite honestly. And for what? Ten or twenty minutes of novelty?

They could have used a harmless, biodegradable chemo-luminescent liquid (similar to that found in fireflies) inside water-soluble, gelatin spheres and gotten the same effect at less cost with a greater choice of colours and at minimal risk to organisms and their environment - and no need to collect 100,000 spheres at the end of the show.

Sigh.