I'm just back from Kuala Lumpur, where I delivered my training course on the operation and maintenance of water and effluent treatment plants to a keen audience.
Just down the road from the venue was the Klang river, which flows through the centre of KL. Whilst it has never been a pure mountain stream ("Kuala Lumpur" means "muddy estuary"), it is clear to both the eye and the nose that it is highly polluted.
There are all kinds of pollution in there. Commercial effluent, industrial effluent, municipal sewage, and simple household and commercial solid waste, some of which you can see floating downstream in my picture.
Clearly Malaysia has a way to go when it comes to cleaning up the environment, but it may not be as far as you might imagine. The smell of the Klang was the same as that of rivers I used to swim in as a boy, which are now so clean that they are trout fisheries.
It does not take long to remedy problems like these, with sufficient money, political will and engineering knowhow.