As far as fishnets and generally discarded rubbish goes. HK has improved in the last 20yrs. Yes, I know that is astounding when considered with many overseas spots. HK is filthy but still cleaner than it was. Air pollution excluded. As far as visibility goes, there was a time when even in areas like Clearwaterbay you could expect no more than 3-4m as a year-round average. I know I virtually lived on a beach there in my teens. When I go back today, I get similar conditions on a bad day. But often it’s surprisingly clear (up to 10m).
I’m not denying anyones observations, far from it I’m agreeing with them. But looking back, I can see improvement. Probably more due to overfishing and losing our manufacturing, rather than any positive action.
I will say that I have seen some bad water quality in my time, and the worst ones seem clearer in my memory. Perhaps because though local pollution has decreased, the surrounding areas have gotten much worse. And if we get a whiff of it now and again water visibility goes down to virtually zero in some places.
Generally though my recent forays back to the ocean were pleasanter than in my youth. The ocean (and you afterwards) doesn’t smell like an ocean, but it doesn’t smell like a factory anymore either.