The Jukskei —no, I'd never heard of it either—is the river through Jo'burg. It joins the Limpopo (the Crocodile, Kipling used both names, just so). For a tributary it is large by comparison with others. It is what we might call an urban river and it is dirty – human dirty, not sediment dirty.
Many rivers in urbanised catchments in South Africa are polluted by raw sewage and effluent to an extent that their ecological function has been severely impaired. The Hennops and Jukskei Rivers lying in the Hartbeespoort Dam catchment are two of the worst impacted rivers in South Africa and are in need of rehabilitation. [73]
Geographers would use the Jukskei as an example of eutrophication (sufficient over-rich in nutrients that it is covered in green goo). This river is everything that an urban river should not be; rich in sewage, heavy in plastic and other human junk waste, prone to flooding, too shallow for traffic and yet with a high flow volume.
I've added a bar graph of pollutants;
Key: medicines (black), psychotropic drugs (red), metabolites (blue box), CNS stimulants (violet), pesticides (yellow) and components/additives (green)
Having read some of the report at [74] I was amused at No occurrence of formal water abstraction for agriculture was encountered in the study area, because that line came shortly after long explanations of the forms of chemical pollution and I'd just noticed the incidence of dip liquor (sheep dip is nasty stuff, you use it in Britain with loads of protection on your body) so that is water you wouldn't want to drink, nor for your animals to drink. And, if you put polluted water on your crops, some of the poisons end up in those crops. It's a poison chain that needs to be broken.
One of the suggestions (recommendations really) would be to use an area of wetland to clean up the water as it leaves the city. This would be only one of many actions: The wastewater from industries can be purified to a certain extent by wetlands. Wetlands are generally very effective in reducing (by up to 95%), the concentrations of nitrogen, pathogenic bacteria and heavy metals in wastewater. However, their efficiency in reducing phosphorous and organic matter concentrations varies widely, with some wetlands removing over 90% and others removing very little. Heavy metals and refractory organic compounds are removed from industrial wastewater by both plant and sediment uptake (Rogers, 1985). Of course, that implies that there is suitable land available and the will to purpose enough wetland to be effective; if there is suitable low ground there are many benefits; not least potential wetland is liable to flooding and so generally not good for habitation, variable in usability for agriculture and purposing it deliberately to continue as wetland (which includes maintenance of it as such) is remarkably cheaper than things like a dam and a treatment plant. You might argue that it is a treatment plant, on the cheap. One could make a case for specialised treatment at the wetland inflow (some of the industrial waste, all of the floating junk (plastic, etc) so that a combination of intervention and allowing enough land area for biology to do the work strikes me as the way to go.
A study of the problem, what is required and suggestions how to achieve (some of) that. This would make a good A/AS Geography case study. I speed-read about half of the 200 pages. The latter end of [74] turns from the Jukskei to the general; how one would manage water resources. It also begs a related study of who has responsibility and how this can be valued enough to be funded properly. The more I read, the more I thought that this si the sort of problem that would be shelved as simply too hard, while never quite becoming important enough to collect even vaguely adequate funding. Until there's an outbreak of cholera or worse, that is, at which point a load of funding is thrown at the problem, which then dries up steadily over time. The supply of money behaves quite often like the water.
I think the underlying problem is the human attitude to waste; once it is 'not here' it is no longer any individual's problem and life for many is simply too hard to have any remaining capacity to look out for the larger social unit. A bit like that office attitude that pushes stuff of one desk onto another; the person with the clear desk thinks they're good at the job; sadly so do others. So downstream is not 'my problem'; I'm offended by upstream behaviour but I carefully don't think about what I do that affects downstream. This is what needs to change and I think that there is a fundamental of our societies that is at fault here. The me-me-me must be displaced with a recognition of contribution to the whole, particularly not damaging that whole. Which might be the aim when schools make consideration part of the declared ethos. This may reduce to one holding responsibility for one's actions, but that implies that there are sanctions only after being caught, where what we need (at the scale of nations) is a collective responsibility—causing individual action—that we value enough to act for the betterment of us all – with the big stick not needed.
DJS 20211202
[72] https://en.wikipedia.org/wiki/Jukskei_River
[74] http://www.wrc.org.za/wp-content/uploads/mdocs/KV202-WEB.pdf