The Causes of Water Pollution

Illustration of black pipe with polluted water running into the sea. Bottles and tons on the sea bottom. Red container ship in the background.

How can pollution of water be prevented?

When we talk about this particular pollution, we are referring to the harmful contamination of streams, rivers, lakes, and seas, by various compounds. As water covers over 70% of the earth’s surface in various forms, aquatic pollution has far-reaching implications, for both us, our environment, and wildlife

Pollution can be naturally occurring, like that from volcanoes, erosion, and forest fires. However, the most concerning types of pollution are those introduced into the ecosystem by humans. Here are some of the most common toxins, along with an explanation of their source and potential effects.

Biological Pollution

This type of pollution means that living organisms have been introduced to a source. They may go on to grow, multiply and eventually become invasive in a particular river or area of ocean. Not all alien microbial life will flourish in an unfamiliar situation, but occasionally they do, adapting quickly to their surroundings and spreading throughout a wider area. Like many other sorts of pollution, biological hazards can make their way into the environment through our intervention.

Human waste is one of the most common biological pollutants, though this is mainly a problem in the developing world. Elements like bacteria or viruses can trigger an epidemic of illness or disease in people who are swimming in, washing or drinking from the affected source. Both typhoid and cholera can be spread in this way.

Oxygen Depletion

This form of pollution describes a lowered amount of oxygen, brought on by the presence of biodegradable matter. Substances like paper, sewage and other waste products from biodegradable processing start to rot when they hit a body of water. Just like in a fish tank, the more oxygen there is, the better aquatic life can thrive in the wild. When this delicate balance is affected, the outcome can be devastating.

When an abundance of decaying material appears in a pond or river, the microorganisms which use it as a food source have more than they need and begin to reproduce at an accelerating rate. More organisms require more oxygen to survive, so this population explosion lowers the levels of oxygen and encourages the growth of anaerobic organisms, those which do not require oxygen in order to live. These go on to produce nitrates, sulfides, and ammonia-like substances which can be toxic to plant life.

When oxygen levels are lowered in a pool or river the first organisms to perish are the smallest. This creates a cascade effect as the entire food chain begins to crumble, soon resulting in larger fish dying. Eventually, other animals like birds or reptiles, which use the area as a food source are also affected. This could be through contact with harmful bacteria, or contaminated fish. Over time the river is abandoned completely, as the wildlife move on to a cleaner area.


Farming is a major factor in nutrient pollution, and it starts with the use of nitrogen and phosphorus to encourage plant growth. Agriculture is a hugely competitive industry and although consumers don’t like to spend a fortune on their weekly food shop, they do expect fresh, uniform and perfect-looking vegetables in their basket. To maintain the appearance and growth of their produce, farmers spray their crops with regular doses of nutrient-rich material, like phosphorus and nitrogen, these usually come in the form of fertilizer.

It’s not just plants which grow on land that seek out nutrients, the same is true for aquatic floras. When fertilizers run off fields into rivers or streams, it can cause plants like algae to bloom and overwhelm the area. As a result, plant life begins to monopolize the river, extracting all the oxygen supplies, resulting in oxygen depletion and the discharging of lethal levels of carbon dioxide.


One of the most well-publicized forms of pollution happens when unwanted chemicals are dumped into a stream or ocean accidentally or intentionally. Some can be pumped into rivers via a factory, or another industrial source like an oil tanker which spills its consignment into the sea. Chemical pollution can also overlap with other forms of pollution, as it can refer to pesticides flowing into rivers from farmer’s fields. Either way, there have been far-reaching effects, from killing off wildlife to making the river toxic to humans. There are three key types of chemical pollution.

Lots of plastic bottles laying on a dark sand beach.


Usually originating from agriculture and industry, metal pollution presents a profuse range of, particularly damaging threats. Many countries in the west, including the USA, have robust laws regarding which metals can be created as a by-product. Unfortunately, many more nations persist in allowing contaminants from metals like nickel, lead, and mercury to be drained into marine areas.

Another substantial source of chemical pollution is badly planned mining programs. When mines are constructed quickly with little thought to forward planning, especially for removing waste, then considerable amounts of metal can leach into the surrounding earth.


Acids and Bases
If a substance has a pH of less than 7, it is classed as an acid. Bases can react with these, and together they alter the pH level in an aquatic environment. This group includes products like solvents which are industrial by-products. Once they are introduced, the pH level can become affected, having a catastrophic impact on the resident animals and fish, and rendering the water undrinkable.


Organic Chemicals
Although we’re familiar with the term organic as meaning something benign, it is one of most the abundant types of pollution across the globe. This type of product is found in many of the items we need to use every day, from our clothes to printing ink, and dyes. They are also used in the pharmaceutical trade, to make medicines and as pesticides in agriculture. Busy industries continue to pump them out at an alarming rate, but consumers can sometimes add to the build-up.

When people fail to use an environmentally sound method to dispose of batteries, mobile phones, and ink cartridges, for example, the cumulative effect is enormous. The second major cause is dumping by factories and the bleeding of crop sprays into nearby rivers and streams. One of the worst cases of agricultural organic pollution came about through the use of DDT, which was developed in the 1940s, becoming one of the first pesticides. It worked perfectly against insects, but quickly filtered into nearby ecosystems, binding with organic materials and leaving massive deposits of noxious organic chemicals.


Particulate Matter
Not all the pollutants that enter a marine area are small enough to dissolve, in some cases, the molecules are just too big to break up fully. These elements are known as particulate matter, or suspended matter, and are a regular source of pollution. Eventually, the tiny particles begin to sink to the lowest section of the river or pond and generate a thick silt layer on the bottom.

Three key problems are triggered during this process; firstly, the small insects, amphibians, fish, and reptiles which inhabit the river bed are harmed or killed. Second, if the suspended matter is made up of biodegradable materials these can swell the number of anaerobic microorganisms, which in turn causes oxygen depletion. Finally, if fish and animals die, the process of decomposition compounds a pollution problem.

Any form of water pollution can represent a serious threat to the environment and our health, that’s why it’s important that contamination is minimal. We can all do our bit by conserving water at home, selecting environmentally friendly household cleaning products and cutting back on the use of pesticides.

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These information were not written by the American Food and Drug Administration, or any other official authority. This site and its products do not promise to diagnose and cure diseases, or protect you from them. Always consult your doctor when you are sick.