When I was a boy I lived in London’s Docklands. Then there were real docks in the East End, working docks which handled imports and exports from London. Despite living in the midst of docks and having many friends whose fathers were dockers, lightermen or watermen, I could only see the river occasionally as most of it was obscured from view by high walls. One of my friends’ father was a policeman, serving on the River police, and he told me that if you fel in the Thames you would have your stomach pumped out, such was the state of the water, filled with poisons and pollution.
Today that part of London has been built upon, forming an extension to the City of London, with high buildings, waterfront views and plenty of views of the famous river. Today, the Thames is much cleaner; if you fall in you will need a towel, rather than your stomach pumped.
Although the Thames is much cleaner than it has been for hundreds of years and the fish are returning in numbers, there is still a problem with the water quality, and this is caused by farming practices. Farmers use nitrates to improve their crop yields and nitrates wash through the land (especially when they are over applied) and find their way into watercourses that run through London. It seems that the United Kingdom’s land has more nitrates run off per capita than that of the land of any other country. Half the excess nitrates run off the land surface and the other half works its way into underground aquifers, and all of it ends up one way or another in the Thames and in the sea. This takes time. Some rules were introduced in the 1990 to prevent using surplus nitrates, but the effect of these rules will not be understood until twenty or thirty years time, when it comes to seeing how successful they have been in preventing nitrate seepage underground.
The problem about nitrates is that they are plant fertilisers and when you enrich waters with plant fertilisers (the process is called eutrophication) you encourage unnatural organic problems in the waters. You increase biomass, particularly algae, who naturally produce certain toxins, the increased algae usually eats up the oxygen in the water (or some of it) making the water a less habitable environment for other water life, increased amounts of weeds grow and there are increased costs in keeping the water navigable and in cleaning drinking water. As the waters warm, so the problems caused by excessive weeds and algae are likely to get worse.
In the words of the old sixties song it is, indeed, a “dirty old river” and we must keep working to clean it up.