That's an often repeated lie. Algae emit O2. It's bacteria eating the unharvested algae that cause CO2 and oxygen depletion, as well as most methane gas.
What's the difference? When you have algae blooms, the stuff dies and suffocates the water and stinks. Just because its the death of it that causes the bacterial problems doesn't mean algae blooms aren't a serious problem.
To me it just evidences the HUGE environmental problems socialist countries cause....FAR MORE than the people in any free capitalist country would put up with....
China isn't much of a socialist country. They don't even have a social security system for retirement. It's the tradition in China that sons take care of their parents in retirement, and daughters take care of their husband's parents, hence the strong preference for baby boys. If you have a baby girl in China you'd better make plans to emigrate to the USA for free retirement.
I suppose you could argue the BP oil disaster was caused by socialist countries: ours and formerly-Great Britain.
As China's wealth grows you'll see growing envy and leftism from within. The leftists will use environmentalism to fight the growing prosperity. Richer countries can afford the high costs of environmentalism.
Algae is not just bacteria food, it's fish food. Tow the algae out to sea where the fish are and can eat it, and you'll have more fish that people can eat. This is a bacteria problem, or a fish food distribution problem, but algae shouldn't be demonized. Algae are probably going to be the future petroleum replacement, allowing capitalism to continue to flourish. For that reason the leftist MSM is already gearing up to always mention algae in the worst possible light.