 Water Pollution In this video, we examine the many ways the substance's mankind throws away have polluted lakes, rivers and even the oceans. The United Nations estimate that around 10% of the world's people do not have access to clean drinking water. That's over 700 million people. The main problem with this untreated water is that it can carry diseases such as cholera spread through untreated human feces. This is particularly serious in shanty towns near big cities and in refugee camps. Rivers and streams can also be polluted with diseases from water coming from badly managed rubbish dumps. But human sewage is not the only substance that pollutes our water supplies. Most of the other substances humans allow to escape into streams, rivers and the oceans are more a danger to natural ecosystems than to us directly. Chemical fertilizers are much more soluble in water than organic manure-based fertilizers, so heavy rain can wash them into streams and lakes, causing eutrophication. The fertilizers cause algae to grow very fast, forming a mat on the lake's surface. This blocks sunlight from the vegetation deeper down, which dies. Bacteria then feed off the dying vegetation and use up the remaining oxygen supply. Once the oxygen has gone, all animal life dies, the lake ecosystem is destroyed. If heavy metals such as lead, mercury and cadmium get into rivers and lakes, many animals will die. In Minamata, Japan, a polluting mercury fungicide factory was closed in 1968, yet people there have continued to be affected by the mercury poisoning, the so-called Minamata disease ever since, because the fish caught locally in the bay still have traces of mercury in them. Nowadays the use of mercury and cadmium in fungicides has been largely replaced by copper and organic compounds. The removal of lead from petrol began in the 70s when it became clear that lead poisoning, causing mental defects, was caused, at least in part, by the lead compounds added to petrol to make it burn more smoothly. It has taken 40 years since then for a United Nations global ban on the sale of leaded petrol. The last six nations complied in 2013. Radioactive waste is normally stored above ground in water tanks, waiting for more permanent underground storage, where it has to be safe for millions of years. There are fears that these underground stores could fail and contaminate water courses. Currently, small amounts of radioactive material are allowed to be washed out to sea on the basis that it will become so diluted that it will make no difference to the natural background radioactivity in the oceans. Following a nuclear disaster like Five Mile Island in 1979, Chernobyl in 1986 or Fukushima in 2011, water courses and the oceans can become dangerously polluted with radioactive waste. During mining and drilling operations to extract minerals from the earth, aquifers, which are the underground water courses, can become polluted. Huge amounts of plastic thrown away from ships and washed out to sea from rubbish dumps on land have ended up floating in huge islands of waste, causing a serious threat to fish, sea birds and other marine animals. The so-called Great Pacific Garbage Patch is estimated to be half the size of Europe, and there are four others. Coal and oil-fueled power stations have been responsible, more so in the past, for causing acid rain, which devastated many North European lakes in the 60s. See our video on acid rain for more on this. Fossil fuel and nuclear power stations need large amounts of water for condensing the steam which drives their turbines. This water is usually cooled on site in the great cooling towers that dominate the skyline of power stations. Even so, the water will be returned to the river or sea warmer than before, and this can upset the river or sea ecosystems. Although not material pollution, this waste heat is a pollutant. So to summarize, there are many ways mankind is polluting the river's lakes and seas. Perhaps the most serious, causing millions to become ill or die, is pollution by human sewage. To learn how we are attempting to purify wastewater and to make water fit to drink, see our linked video, Water Treatment.