>>105137769The Thames is one of the cleanest rivers through any major city in the world. It's brown because it runs through a major sediment bed as the plain on which London sits is mostly loam.
Compare that to the Hudson, for example, which is so full of polychlorinated biphenyls even today that you'll get cancer if you eat what you fish there. Even if you don't, you'll get chloracne from the PCBs, and if you've eaten enough of them, when you use up the stored fat reserves of your body - even if you're not a huge fatty - you can release so much of them direct into your bloodstream they can cause major damage to your organs. Amazingly the company that originally dumped them into the river argues that it shouldn't have to clean them up, because while they're just buried in the river bed being eaten by various parts of the food chain they're less harmful than if the river bed were dredged and cleaned.
