July 13, 2024

I, Science

The science magazine of Imperial College

Andrew Purcell

Some shocking statistics about the world’s rivers:

  • Every day, 2 million tons of human waste are disposed of in water courses. (Source: World Water Assessment Programme (WWAP))
  • In developing countries, 70 percent of industrial wastes are dumped untreated into waters where they pollute the usable water supply. (Source: WWAP)
  • Projected increases in fertilizer use for food production and in wastewater effluents over the next three decades suggest there will be a 10-20 per cent global increase in river nitrogen flows to coastal ecosystems. (Source: Global Environment Outlook: environment for development (GEO-4))


Of course, polluting our rivers isn’t just detrimental to human health; it can also be devastating for the wide range of species which depend on river habitats. Below are some of the major ways in which river species are threatened:


Surface mining, timber harvesting, construction, and poor farming practices can all leave soil unstable. When it rains, the soil is then easily carried off into rivers and streams. The resulting muddy water does not allow light to penetrate deep enough into the water for use by plants and other aquatic life.

Acid Rain

You might not realise, but acid rain is still a major problem for the world’s rivers. This is a particular problem in some areas of North America. The northeast U.S., the Rocky Mountains, areas of the north-central and southeastern U.S. and eastern Canada are all severely affected by acid rain. Once a body of water becomes too acidic, the organisms in the water’s food chain begin to die. Eggs and larvae are sensitive to low pH and are often unable to survive. As water becomes more acidic, the fertility of eggs is reduced, fewer hatch, and fish may not grow to adult sizes. Eventually, fish or insects, the fish’s food, may no longer be able to live in water with a low pH.

Agricultural Waste

Fetilisers and other organic materials produced by agriculture can threaten fish when they flow into lakes and rivers, via a process known as eutrophication. An brief explanation of this process can be found here.


Raw sewage can cause serious diseases in humans who use the water or eat shellfish from polluted areas. Sewage may also make waters unhealthy to swim in. Whilst robust environmental protection laws mean that raw sewage isn’t usually a problem in the developed world, the main problem linked to sewage is that it also causes eutrophication.

Industrial Waste

Again, this can be a cause of eutrophication. Industrial wastes may also contain toxic chemicals. Therefore, it is vital that industrial waste is treated before it is allowed to enter water systems. Usually, this is the case in the developed world. But, more stringent government legislation is needed in many developing countries to ensure industrial waste is always treated in these areas too.

Oil Spills

Oil spills can have disastrous effects on aquatic life, often killing by direct contact with fish’s gills. Oil may also suffocate eggs and young fish, since the young inhabit shallow waters where oil tends to concentrate. Birds, otters and other river species may also be killed.


As well as making rivers unsightly, food packaging and other products discarded in rivers can threaten organisms which survive in this habitat. Plastics are particularly hazardous. They are not easily biodegradable and can stay around for a long time, potentially for hundreds of years. In the U.S. alone, thousands of fish and birds die every year from entanglement in the plastic six-pack rings that come from canned drinks.

Invasive Species

As well as climate change altering the range of many species worldwide, sometimes fish are actively introduced into new rivers and lakes for sport. If done carefully, this is often not a problem for the local ecosystem. However, if done recklessly, such introductions can upset the delicate balance of the river or lake ecosystem, causing major potential harm.


Last  month, the UK government announced £92m of funding to help clean up our waterways: