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Substances Causing Pollution in Rivers 

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The substances that cause water pollution can be divided into two main groups - germs and chemicals. Germs are small organisms that cause diseases such as malaria, cholera and bilharzia, and chemicals are poisons, which are mainly produced by industries. 

1. Possible Poisonous Chemicals in River Water

Natural chemicals are found everywhere in the environment. Unfortunately, many of the chemicals that are produced by industries are not found naturally in the environment or are only found in very small amounts. Different industrial processes produce different types of products and waste products. Unfortunately many industries release their waste products directly into rivers or let them leak into the groundwater. These chemicals are poisonous or toxic to plants, animals and people. Some examples are:


Insecticides are chemicals that are sprayed onto crops to kill the insects that eat crops. One of the more controversial insecticides is DDT. The use of DDT on crops was used to control the malaria mosquito in South Africa. At certain levels (10 mg per kg) DDT can cause human poisoning with the following symptoms: dizziness, vomiting and convulsions. At lower levels, DDT can affect the development of babies and has been associated with cancer. DDT has been banned in South Africa. Another group of controversial insecticides are the organo-phosphates. These insecticides have been used in the place of DDT since it was banned. Some specialists believe that these insecticides have caused even greater environmental damage than DDT and that they are even more toxic to humans and other mammals.

Insecticides are easily washed by the rain into streams and groundwater where they poison fish and domestic animals. Many insecticides are stored for a long time in the bodies of animals and can end up in the meat, fish, egg and milk that you eat. Fruits and vegetables that have been sprayed with insecticides also remain poisonous for many days afterwards and must be washed very well before eating.

Ask questions about the use of insecticides in your area. Keep a look out for fish or birds that have been poisoned. Dead fish and birds provide a good indicator of chemical pollution. If you suspect pollution by insecticides then contact your local council as soon as possible.

Heavy Metals

Heavy metals such as nickel, molybdenum, zinc, cadmium and lead are mined and processed by the mining and ore-smelting industries, many of which occur in Gauteng. These metals are easily washed into streams and groundwater. Copper and mercury are another two heavy metals, which are found in fungicides. Fungicides are also sprayed on crops and easily washed into rivers. These heavy metals are toxic to biological life including the people who may have to drink from the polluted rivers. Crops that have been irrigated with polluted water can also be dangerous. In a similar way to DDT, heavy metals can also build up in the body causing symptoms of poisoning.

In the past, toxic waste products were dumped into the rivers or into landfill sites close to where people lived causing health problems and even death. Today all South Africans have a constitutional right to a clean and safe environment. Make sure that you remain informed and observant so that you can prevent toxic chemicals from being used in your environment. If you suspect water pollution in your area then contact your local council.

Problem Products

We all know about the destruction that oil pollution causes along the marine coastline. However, a lot of oil pollution also occurs inland. Petrol and diesel is stored in underground tanks at petrol depots. When these tanks are not properly maintained, they can develop cracks allowing the petrol to leak out. Many people are also very negligent when changing the oil in their car engines. Many people just throw the oil onto the ground! This oil and petrol is washed by the rain into the groundwater. This ground water eventually surfaces at boreholes and wetlands. In the past, groundwater was considered clean since chemicals and germs were not present, but this is changing very quickly. Groundwater is becoming more and more polluted with a number of toxic substances including insecticides, petroleum products and heavy metals. South Africa is a dry country and as the human population grows, our groundwater is becoming very valuable. We must all work towards keeping this resource as clean as possible for the future when we really need it.

Chlorine and Detergents

Paper and pulp mills and textile factories are amongst the worst water polluters. Paper and pulp mills use up large amounts of water and produce a lot of polluted wastewater. The wastewater contains strong chemicals such as chlorine, which is used to make paper white and soft. Textile factories also release strong chemicals like caustic soda, acids, dyes and detergents into water. These strong poisons also cause bird and fish kills similar to insecticide poisoning. These chemicals are also directly poisonous to humans. Ask questions about what industries occur in your area and how they release their wastewater. Do not drink water that is downstream from a factory that releases wastewater into the river.

Remember that the detergents that you use at home are just as poisonous so use only biodegradable products. Read the label on the product that you are buying; this will tell you what the product is made of and if it is environmentally friendly.

2. Fertilisers and Sewage

Some chemicals like fertilisers are made of substances that do occur naturally in the environment, but only in small amounts. When too much fertiliser is washed from farmlands into a river then that water will also become polluted. Human sewage or cattle excrement that is untreated also causes water pollution in the same way as fertilisers do. Human sewage also contains germs that cause diseases such as hepatitis and cholera. Soaps and washing detergents contain both natural and man-made (artificial) chemicals. Artificial chemicals like bleach and chlorine were discussed earlier. The natural chemicals can cause a pollution problem similar to that caused by fertilisers.

Phosphates and nitrates are found in fertilisers, sewage and soaps. Phosphorus is an essential element for life, both as a nutrient for plant life and as a key element in the metabolic processes of all living things. The normal low phosphate (PO4) level in water inhibits the growth of plants but a small increase of phosphates can result in a rapid increase in plant growth such as blue-green algae and water hyacinth, especially in dams. The water plants become overcrowded and die. When they die the decomposing bacteria uses up more oxygen and affects other forms of life badly, eg. fish suffocate. This process is called eutrophication, and can be increased by human activities, eg. domestic effluent (especially soapy water), farm and lawn fertilisers, industrial effluent and the destruction of wetlands.

Nitrogen in the form of ammonia (NH3) and nitrates (NO3) form part of the plant nutrients that can lead to eutrophication. Nitrate enrichment through sewage contamination and fertiliser runoff is not as critical as it is with phosphates because aquatic ecosystems are not as sensitive to increases in nitrate levels. Nitrogen normally occurs in a form that plants cannot use (i.e. nitrogen gas), however, it may be used in the decomposition of dead water plants and by blue-green algae which can convert nitrogen in the air into ammonia and nitrates that plants can use. This subtle interdependence illustrates the complexity of the relationships within an aquatic ecosystem. The best way to stop this kind of pollution is to prevent human sewage, cattle excrement and fertilisers from washing into rivers.

Blue-Green Algae
Blue-green algae are microscopic inhabitants of rivers. They liberate oxygen into the water, take up mineral nutrients and produce substances which enter and support food chains in the aquatic environment. With a rise in river pollution there is an increase in nutrients. This causes a great increase in the growth of blue-green algae, which are called algal blooms. These blooms have an effect on the colour, taste and odour of rivers. Human contact with these algal blooms can cause illness, such as hayfever, skin rashes, eye irritations, vomiting, gastroenteritis, diarrhoea, fever and pains in muscles and joints.

3. Water Pollution and Disease

Most diseases in the world are related to water and sanitation. To break the cycle of disease, there must be improvements in the quality of water that people use. Most rural communities in South Africa do not have access to running water, toilets or latrines and they use watercourses for defecation and urination. In many cases, where they are present, latrines are situated upstream from where the community collects their water supply. Faecal pollution of water increases the risk of infection of various diseases to those using these courses as their life supporting water source. Groundwater, which is another water source, can become contaminated through unclean irrigation water. Water related diseases could be spread in other ways, which also affect urban communities, such as insect bites and poor hygiene.

Although there are many more, these are some of the most common water – related diseases in South Africa:


This occurs, like most diseases, in a cycle with a parasite and different hosts. Bilharzia only occurs in areas where conditions are right for the parasite to be able to complete its life cycle. The adult parasite is a worm that lives in the bladder or intestine of humans (the main host). They mate inside the body and eggs are released in the urine or faeces of the host. If an infected person defaecates and urinates into the water, the eggs hatch into the swimming form of the parasite. It then burrows into the body of a snail (the intermediate host). The snails favour slow moving water with plenty of vegetation. Here the parasite changes form and exits out into the water again. This is the stage that infects humans. If a person has contact with contaminated water the parasite will penetrate their skin and move through the body causing illness. Some symptoms of Bilharzia: an itchy rash, headaches, abdominal pain, diarrhea, bladder infections, fever, enlarged liver and swollen veins. Within South Africa, Bilharzia is most common in the Northern Province, the Lowveld and KwaZulu-Natal.


In South Africa Malaria is given very high priority. This disease, which also occurs as a cycle, is caused by a parasite that is transmitted by some species of female mosquitoes. The female mosquito requires a blood meal in order to obtain sufficient energy and nutrients to produce her eggs. When a mosquito bites a human, it injects saliva into the bloodstream to prevent the blood from clotting. If the mosquito is infected with the malarial parasite, the parasite will be released from the mosquito’s saliva into the blood of the human. The parasite travels through the body and enters the red blood cells. The red blood cells eventually burst releasing the parasite into the blood stream where it is ready to be sucked up by the next mosquito. Mosquitoes breed in water, especially dams, ponds, water tanks, old car tyres, and other hollow objects that can hold water, like tins. The best way to protect yourself from Malaria is not to leave litter lying around, and to prevent getting bitten by wearing long sleeve clothing and by applying insect repellent to your skin, especially at night. Some symptoms of Malaria: fever, headache, diarrhoea, nausea, joint and muscular pains, shivering, sweating and fatigue. Malaria is distributed in the Northern Province, Mpumalanga, Northern KwaZulu–Natal and parts of the northern Cape.


Cholera is a disease that is caused by bacteria (Vibrio cholerae) that is spread through water contaminated by faeces from an infected person. The bacteria produce a toxin that causes the small intestine to secrete large amounts of fluid, which leads to fluid loss, i.e. diarrhoea and vomiting. People who do not wash their hands after using the toilet can spread the disease. It can also be spread when human faeces are used as a fertiliser for vegetable crops. It is important to remember that even if a person does not show symptoms of the disease, they could still be infected and spread the disease. Cholera can be found in most places where there is poor sanitation. Some symptoms of Cholera: diarrhoea and vomiting. People who have the disease should drink plenty of clean water to prevent dehydration.

Important Things That You Can Do to Decrease the Risk of Disease

  • Do not defaecate or urinate near water sources;
  • Wash your hands with soap and water after going to the toilet;
  • Do not drink water that you think might be unclean - boil it if you are unsure;
  • Wash all fruit and vegetables well before eating them & do not cook with unclean water;
  • Do not leave empty containers or any litter lying around for disease transmitting insects to breed in;
  • If you have access to pit latrine facilities, ensure that they are away from sources that are used for drinking and bathing. The pit should not penetrate groundwater.

See also

Rural Water Purification
Water Pollution and Your Health
Water Situation in South Africa