Test Your Knowledge Flash Cards 🔒Play Lemonaire 🔒Play Last Stand

Rivers: Opportunities and Hazards » River Pollution: Causes and Impacts

What you'll learn this session

Study time: 30 minutes

Cambridge spec: 1.3.5, 1.3.6

The human causes of river pollution, from sewage to plastics
How fertiliser leads to eutrophication, step by step
The difference between point and non-point sources
The social, economic and environmental impacts, and how they differ in LICs and HICs

🔒 Unlock Full Course Content

Unlock This Course

What is river pollution?

A river is a free delivery service. It carries water, sediment and anything else that gets into it. When people add harmful substances or heat to a river, the water becomes polluted and is less safe for people and wildlife. Most serious river pollution comes from human activity, and that is what this lesson is about.

Key terms:

River pollution: harmful substances or heat added to a river by human activity.
Point source: pollution that enters the river at one clear place, such as a pipe.
Non-point (diffuse) source: pollution that enters from a wide area, with no single pipe or place.
Eutrophication: too many nutrients in water, leading to a huge growth of algae and then a fall in oxygen.
Bioaccumulation: a poison building up in living things, so animals at the top of the food chain get the biggest dose.

The human causes of river pollution

Here are the main causes. Learn the cause, what it puts in the river, and where it comes from.

Cause	What gets in the river	Where it comes from
Untreated sewage	Germs and waste from toilets	Towns with no treatment works, or drains that overflow
Industrial waste and chemicals	Metals, dyes, acids and other poisons	Factories, for example textile dyeing
Farm runoff	Fertiliser and pesticides	Fields washed by rain
Mining waste	Toxic metals and muddy water	Mines and spoil heaps
Plastics and litter	Bottles, bags and tiny plastic pieces	Dropped litter, overflowing bins, rubbish dumped on banks
Thermal pollution	Warm water	Power stations that use river water for cooling
Oil and urban runoff	Oil, petrol and road dirt	Roads, car parks and leaking vehicles, washed in by rain

Thermal pollution is easy to forget. Warm water holds less oxygen than cold water, so a river heated by a power station can be bad for fish even though nothing poisonous was added.

Point and non-point sources

🏭 Point sources

One place, so easier to find and stop. A factory outlet pipe or a sewage pipe are examples.

🌾 Non-point sources

Many small places, so much harder to trace. Fertiliser washing off fields and dirt washing off roads are examples.

Think of a leaking tap compared with rain dripping through a whole roof. You can fix the tap. The roof is a much bigger job.

Eutrophication in numbered steps

Fertiliser is meant to help crops grow, but rain can wash it into the river. Write the process in this order in the exam:

Rain washes fertiliser from fields into the river as runoff.
The river now has too many nutrients, such as nitrates and phosphates.
Algae grow very fast and cover the surface. This is an algal bloom.
The bloom blocks sunlight, so plants below the surface die.
Bacteria feed on the dead plants and algae and use up the oxygen in the water.
With low oxygen, fish and other animals die.

The impacts of river pollution

Impacts can be sorted as social (affecting people's lives and health), economic (affecting money and jobs) and environmental (affecting nature). They can be felt at every scale: local (a village), regional, national and global.

👨 Social

Water-borne diseases such as cholera and typhoid. Unsafe drinking water. Loss of safe places to wash, swim or play.

💰 Economic

Fishers and farmers lose their livelihoods. Water companies pay for expensive treatment. Tourism income falls.

🌿 Environmental

Fish deaths, loss of biodiversity, algal blooms and low oxygen. Poisons build up by bioaccumulation.

Pollution can also travel. A river carries it downstream to other towns, other regions and sometimes into another country or the sea. A problem that starts locally can become a regional or national one.

Bioaccumulation

Some poisons, such as mercury, are not broken down. Small animals take them in. Fish eat many small animals, so the poison builds up in the fish. Birds, otters or people who eat a lot of fish take in the strongest dose. In Minamata Bay in Japan (a sea inlet, not a river), mercury waste from a factory built up in fish and made many local people seriously ill. Rivers can carry poisons in just the same way.

Examples from around the world

Lake Erie, North America (HIC): nutrients carried in by rivers fed an algal bloom in 2014 that made the drinking water of the city of Toledo unsafe for a few days.
Citarum River, Indonesia (MIC): factory waste, including from textile mills, and household rubbish have made it one of the most polluted rivers in the world.
Cuyahoga River, USA (HIC): oil and industrial waste on the river caught fire in 1969, which helped to start the clean-up movement.
Rio Doce, Brazil, South America (MIC): in 2015 a dam holding mining waste collapsed and the waste flowed down the river towards the sea, killing fish and cutting water supplies to towns.
Niger Delta, Nigeria, Africa (LIC): oil spills have polluted creeks and rivers, harming the fishers and farmers who depend on them.
River Rhine, Europe (HIC): in 1986 a fire at a chemical warehouse in Switzerland sent chemicals into the river and killed large numbers of fish.

LICs and HICs: why the impacts differ

The same pollution does not hurt everyone equally.

In many LICs, more people take water straight from the river for drinking and washing, and sewage treatment is often limited. So disease and deaths are higher, and families lose both income and health.
In HICs, most homes have safe tap water and treatment works. The main impacts are the high cost of treatment, damage to wildlife and lost recreation and tourism.

Common mistakes

Saying pollution "kills the river" without saying how. Always give the chain: fertiliser, algae, low oxygen, fish deaths. Also, do not mix up causes (what puts it in the river) with impacts (what it does). Finally, remember that this lesson is about causes and impacts, so leave out how pollution is managed.

Exam-style question

Fig. 1.1 shows made-up data for the River Delmar, measured on one day in summer.

Site	Position	Oxygen in water (mg per litre)
A	Upstream, before the town	9
B	Below the town sewage pipe	3
C	Below farmland	5

(a) Identify the site with the least oxygen. [1 mark]

(b) Explain how fertiliser from farmland can reduce the oxygen in a river. [4 marks]

Model answer

(a) Site B (1).

(b) Rain washes fertiliser into the river (1). The extra nutrients make algae grow fast, forming an algal bloom (1). The algae block light so plants die, and bacteria use up oxygen as they feed on the dead material (1). The low oxygen means fish die (1).

(c) A top-level answer gives balanced social, economic and environmental points, explains each one, and reaches a judgement. For example: People are affected socially because polluted water spreads diseases such as cholera, especially where people drink straight from the river (1). Economically, fishers lose their catch and farmers cannot use the water, and treating drinking water costs a lot (1). The environment suffers because fish die from low oxygen and biodiversity falls (1). Poisons can also build up in the food chain by bioaccumulation, so animals at the top, and people who eat fish, get the largest dose (1). The impacts are often worse in LICs, where more people have no safe alternative to river water (1). Overall, the harm to people and wildlife is serious, though it can be reduced where there is money for treatment (1).

Exam tip

In a "Discuss" answer, name at least one social, one economic and one environmental impact, and give a reason for each. Use the word "because" often.

Test Your Knowledge