There appears, here, to be a ...

There appears, here, to be a reluctance to accept the obvious. For a river to become self-purifying you have to reduce the pollution loading to a point where the river can recover naturally. Whilst wetlands will work, there's one near me, the Ganges is too big for this. Aeration can be effective but has limited effect if it is not sufficient to address the underlying problem. To make self-purification work there are four basic things that have to be done:
1. reduce sewage loading through the construction and operation of municipal treatment plants;
2. control industrial waste discharges;
3. reduce the excessive use of agricultural fertilizers and pesticides;
4. address the problem of leachate from solid waste sites.