Great article: [Ruamahanga: the story of a river](https://i.stuff.co.nz/environment/98873908/Ruamahanga-the-story-of-a-river)
Despite the continual drum it's farmers who pollute our rivers, we learn from this story:
> The first town the Ruamāhanga flows past is Masterton, Wairarapa's biggest town. It's here that it encounters the first of the sewage treatment plants, which have been a major cause of the river's woes in the past. It's not hard to see where the river's unkind nickname, the "Sewer-mahanga," comes from.
Wow. It's the city dwellers who dump their sewage in the rivers. Very salient, as Auckland has just applied to continue to dump its storm water unto our beaches.
Storm water is a different problem to sewage. It should be relatively clean although road water is often contaminated with road grime and lazy peoples oil change residue.
Sewage though is something we should not be proud of. Go back 50 years and very little town sewage was treated to any real standard before being dumped in the sea or rivers. Still when the population was less than 2 million the rivers could handle it. In most cases you could still fill a glass of water 100 meters below the outfall and drink it. Now most towns have some sort of treatment but not all are up to the job and even the best ones fail every now and then. Then there are the factories. Dairy and meat are big culprits. You would probably find that 1/3 of dairy polution isnt the farm its the factory at the end. As for meat works I remember fishing below the outfall from the Finigand meat works Big trout could be had but they were quite fussy. I remember storys about the Matarura meat works. Huge fish in that river and they were totally uninterested in any normal bait