I was flying into HCMC last month and was glued to the window as the plane descended. About 10 minutes before landing, I was looking down and saw perhaps a dozen very big patches of either land or water that were glowing green far below the aircraft. I thought they might be lakes with bioluminescent algae, but the light struck me as being artificial. It was entirely regular. It was a lot like the look of those old Timex watches (the backlit, not side-lit kind) when you press a button and the panel lights up with that dim greenish glow. These patches of glowing, greenish light were huge—each of them many acres in size.

 

Anyone have a clue what I was looking at?

prawn/fish farms, or aquaculture .

Fireworms?   https://www.livescience.com/5388-clues-sea-green-glow.html