Tourism in Halong Bay has been a tragedy, most of it invisible. The karsts shooting out of the water are difficult to build on, so they are still green and undeveloped, but the water is polluted and the fish stocks decimated. The fishing that is done is, by all accounts, far less than what it used to be.
What is most visible and most visibly tragic are the monkeys on Monkey Island, who swarm tourist boats and beg for food or drinks. They seem to subsist on candy, chips, and bottles of soda, which they can open, either by twisting the caps or ripping the bottles on rocks, If they’re not given these things outright from tourist hands, they will steal them, then fight over the carbs and sugar. They’re like little kids, but with worse manners.
If you ignore the human destruction, the bay is stunning. The floating villages were incredible. Apparently much of the development that DOES exist is because of remittances sent back from relatives who have moved to America and send money to their families.