Yeah, the litter in South East Asia is a big problem. The litter really bothered me in Thailand and Laos, but by the time I got to Vietnam I didn't notice it as much. I guess I just got used to it after a few months.
There are some interesting theories about why the litter is so bad out there. The one I like the best is that the cultures down there have been throwing their trash on the ground for hundreds (thousands?) of years. This wasn't a problem until trash started being made out of plastic instead of banana peels and coconut husks.
They really need more public awareness about litter. I was at a waterfall in Laos and a lady opens an ice cream for her kid, then throws the wrapper on the ground. Right next to a trash can. She had probably traveled for hours to go to a beautiful place that wasn't full of trash like her home, and here she was bringing the trash with her.
Yeah. I was most disappointed at Halong bay. One of the most beautiful places on the planet. But litter everywhere in the water.