Polluted Water

Have you ever been to the Lake District? It's the biggest National Park in England, and also home to a single lake, one of the biggest in the UK, and the deepest in England. Recent water pollution, however, is resulting in the breakdown of aquatic ecosystems in Lake Windemere. Private septic tanks and inappropriate waste disposal from plants are causing an influx of dangerous chemicals and nutrients. This poses a risk to both aquatic life and humans.

Polluted Water Polluted Water

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Table of contents

    There are lakes, rivers, and oceans all over the world that are being threatened by water pollution. Today we are going to be looking at some examples of water pollution, how water pollution is caused, and the effect polluted water has on human populations and ecosystems.

    lake district sunset, polluted water, StudySmarterFig. 1. The Lake District at sunset. Source: Unsplash.

    • What is water pollution?
    • Examples of water pollution
    • Causes of water pollution
      • Wastewater treatment
      • Agricultural runoff
      • Industrial Discharge
      • Urban runoff
      • Acid rain
      • Global warming
    • Effects of polluted water
    • Solutions for water pollution

    What is Water Pollution?

    Water pollution is the alteration of the natural composition of a body of water. This can be by the addition of chemicals, metal particulates, radioactivity, or even heat. Some natural causes can result in water pollution however human activity is the major driver behind the contamination of global waters.

    There are two types of pollution: point-source pollution and non-point source pollution:

    Point source pollution is contamination that can be attributed to a certain area or exact point. Sewage pipes and industrial discharge channels are examples of pollution which can be pinpointed.

    Non-point source pollution is contamination that stems from a general area and can be difficult to quantify. Examples of non-point source pollution are runoff from agricultural areas and acid rain.

    Governments will find non-point source pollution difficult to attribute and control directly, so strict laws and legislations must be put into place to reduce the general release of pollutants.

    For example, the Clean Water Act (CWA) in the US1, passed in 1972, regulates the emission of water pollutants, including non-point pollution. One of the most affected landscapes by unregulated water pollution in the US was wetlands. The regulation of water pollution through the CWA helped protect not only drinking water but also the wetlands.

    Wetlands, polluted water, CWA, StudySmarterFig. 2. Wetlands. Source: Unsplash.

    Examples of water pollution

    Let's have a look at some examples of water pollution:

    • Fertilisers: agricultural fertilisers normally contain large amounts of nitrogen and phosphorus and can runoff into nearby rivers, lakes, and oceans if by the coast. These elements are beneficial in small amounts but will harm aquatic ecosystems when waters become inundated with them.
    • Pesticides: other agrochemicals farmers use to deter natural pests may also runoff into nearby waters after rainfall. These chemicals can often be poisonous to many different species.
    • Sewage: poorly managed sewage can seep into nearby waters and often contains large amounts of nitrogen and phosphorus.
    • Industrial waste: discharge from industrial areas can contain a variety of toxic and radioactive chemicals like crude oils, metal particulates, acids, alkalis, solvents, and PCBs (polychlorinated biphenyls).
    • Pathogens: the addition of disease-carrying microorganisms and viruses can also pollute waters.
    • Heat: waste heat from industrial plants and global warming can cause dangerous increases in water temperature.

    In theory, you can consider the introduction of non-native species to an aquatic environment as water pollution. This can occur by humans physically carrying alternative species into the habitat, or climate change forcing species to migrate to more suitable habitats. These species will take up space, compete for resources, and potentially become novel predators, which can seriously disrupt an ecosystem's balance.

    Eutrophication is a process we cover a lot, but it is one of the worst consequences of polluted water. An influx of nutrients from agricultural runoff, industrial runoff, or sewage will cause algal populations to increase at a rapid rate. This will lead to a phenomenon called an algal bloom, which covers the surface of the water. These algal blooms will block the penetration of sunlight into the ecosystem and when they are broken down by aerobic decomposers, the available oxygen will be sucked up. This severely disrupts the ecosystem of the river or lake affected by an algal bloom.

    Algal bloom, eutrophication, polluted water StudySmarterFig. 3. Algal blooms prevent the sunlight from reaching deeper parts of the water, causing plants below the surface to receive less light. Increased oxygen consumption will reduce the chances of other species to respire in the water. Competition for resources will be harsher and the environment will suffer from a lack of nutrients. Source: Unsplash.

    Causes of Water Pollution

    So now we know the different types of water pollution; what causes the addition of these substances to the water? There are six main causes for water pollution:

    • Wrong wastewater treatment
    • Agricultural runoff
    • Industrial discharge
    • Urban runoff
    • Acid rain
    • Global warming

    We'll have a look at each of these causes in more detail in the sections below.

    Wastewater treatment

    In highly populated areas, massive amounts of human and animal sewage are treated daily. This sewage will contain animal faeces and detritus, so will contain lots of organic nutrients and lots of bacteria. The disease-carrying pathogens will pose a threat to human health, while the decomposing bacteria will suffocate the waters of their oxygen and release lots of nutrients. Sewage treatment facilities are often focused on eliminating some of the dangerous chemicals that can be released into the water like oils, metals, acids and alkalis, rather than the seemingly less dangerous bacteria and organic nutrients. However, the combination of decomposing bacteria and nutrients is harmful to entire ecosystems and the quality of drinking water.

    Detritus is waste of any kind, and often refers to animal excrement or dead organic matter.

    Agricultural runoff

    Farmers need to produce enough food to feed the population and earn money to make a living, so the environmental implications of their methods are not always considered. The overuse of artificial fertilisers and pesticides is endangering nearby aquatic ecosystems. Agricultural fertilisers contain nitrogen and phosphorus for plant growth, so you can imagine how much is needed for a field of crops (then think about entire agricultural regions!). After rainfall, the water (containing nitrogen and phosphorus ions not taken up by plants) will run off into nearby aquatic waters, which can cause oxygen depletion. Pesticides will also be present in the runoff and will contain poisonous chemicals as their purpose is to kill and deter species.

    agricultural runoff, artificial persticides and fertilisers, StudySmarterFig. 4. Can you imagine the amount of artificial fertilisers and pesticides that is needed to optimise the production of this field? And this is only one farmland! Source: Unsplash.

    Regenerative agriculture practices sustainable methods which aim to maintain and improve soil quality. Healthy soils will produce greater yields and larger crops. Regenerative practices include limiting physical disturbance of soils (such as tillage), covering soils with temporary crops, and leaving perennial wild crops. Healthy soils will require fewer fertilisers and pesticides, so reduce water pollution in the area too.

    Industrial Discharge

    Industrial processes involve the use of chemicals and particulates which are poisonous, radioactive, or carcinogenic in water. Runoff from industrial areas and poorly treated industrial waste will contain large amounts of dangerous metal compounds (mercury, aluminium, chromium), radioactive chemicals (uranium, plutonium), and acidic compounds. The discharge of cooling water from power plants can cause heat pollution as well. Despite being called 'cooling water', it is much warmer than the water in lakes, rivers, and oceans, and can cause drastic changes in temperature which can have a knock-on effect on ecosystems.

    Oil spills are the most catastrophic example of industrial discharge. They can completely change the composition of water: shifting pH levels, releasing poisonous chemicals, and causing hypothermia.

    The combination of agricultural, industrial, and runoff can form dangerous sedimentation that piles into coastal ecosystems. Sediment influx can introduce massive amounts of nutrients and smother benthic organisms (organisms that live at the bottom of the body of water), killing many species and providing the conditions for the rise of producers which lack the provisioning value to form stable foundations of aquatic ecosystems.

    Urban Runoff

    In densely populated urban areas, dumped litter and waste can make their way into nearby waters. Improperly disposed waste from cities and general public litter in the form of plastics, food, metals, and electronics can contain all sorts of toxic and radioactive chemicals (metal compounds, hydrocarbons, solvents). The degradation of waste only releases more of these chemicals.

    Underdeveloped countries with smaller populations still produce massive amounts of waste because of their limited laws and companies involved in removing waste.

    Acid Rain

    Acid rain is rain that has turned so acidic that it causes harm to the environment.

    Nitrous oxides and sulphur dioxide emissions from power plants can cause acid rain. These gaseous particles will react with water vapour molecules in clouds to form nitric acid and sulfuric acid and then fall as acidic precipitation (pH < 5.2). Acid rain can pour directly into waters and increase pH or runoff from soils and carry harmful chemicals with them.

    An increase in pH increases the likelihood of poisonous aluminium ions being isolated from aluminium hydroxide in soils. Aluminium ions stunt root growth in plants so can affect producer populations when they run into water.

    Evaporating polluted waters (containing nitrate ions) can cause acid rain too.

    Global Warming

    Anthropogenic global warming is causing heat pollution of waters. Many marine species become stressed in warmer environments and require more oxygen to match their increasing metabolic rates. Carbon dioxide (CO2) emissions are causing ocean acidification as well, which reduces carbonate availability. Organisms with calcareous shells and exoskeletons require carbonates to survive.

    Crabs, polluted water, studysmarterFig. 6. Crabs are one of the species that have an exoskeleton and can be affected by a reduction in carbonate availability. Molluscs and other bivalves also suffer from a lack of carbonate.

    Carbon dioxide dissociates to form carbonic acids, which then react with carbonates to form bicarbonates, which are not very useful!

    Effects of Polluted Water

    As you can imagine, with water being such a crucial part of human and wildlife life, polluted water causes severe problems for the ecosystems and for the human species. Check out our Impacts of Polluted Water article for more detail, but here are some of the consequences of polluted water:

    • Algal blooms can affect entire aquatic ecosystems and can even result in anoxic 'dead zones' where no life can survive.
    • The breakdown of algal blooms can release poisonous toxins that harm wildlife and can spoil drinking water.
    • Sedimentation fluxes from agricultural and industrial runoff can severely affect coastal ecosystems by smothering producer populations and adding an excess of nutrients.
    • Water polluted from fertilisers and sewage can contain nitrate ions, which form acid rain after evaporation and condensation.
    • Debris from litter can physically disrupt and trap organisms.
    • Dangerous microorganisms can spread disease in aquatic ecosystems.
    • Rising temperatures increase stress on aquatic organisms and cause disease to spread quicker.
    • Many metal compounds are toxic and can poison wildlife.
    • Carcinogenic and radioactive chemicals can lead to the rise of mutations and the breakdown of populations.

    Solutions for water pollution

    There are many solutions to prevent water pollution, this can be by introducing widespread regulations or by stopping a point of serious pollution. Here are some examples:

    • Daily water conservation: water is a limited resource and essential for everyday life, so conserving water by turning off taps and limiting showers will save money and reduce pollution.
    • Sewage treatment: the appropriate treatment of liquid waste is necessary to reduce water pollution. Many sewage treatment systems focus on the removal of toxic chemicals and particulates, but implementing methods to remove nutrients and microorganisms could limit pollution massively.
    • Agriculture: limiting the use of pesticides and fertilisers in agriculture is needed to reduce water pollution of nearby waterways. Transitioning to sustainable and regenerative agricultural methods will help lessen the need for agrochemicals.
    • Renewable energy: changing to renewable energy sources will reduce the amount of waste released from factories and power plants.
    • Stormwater management: powerful storms can increase the rate and unpredictability at which water runs off. Reverse osmosis, sand filtration, and simple blockades can help limit the runoff of polluted waters.

    Remember the difference between point source pollution and non-point source pollution. The strategies to combat each type of pollution will depend on the source and how easy it is to pinpoint the source.

    Hopefully, you now know more about water pollution. Remember that water pollution is the alteration of the natural composition of a body of water and can be caused by humans but also by natural causes.

    Polluted Water - Key takeaways

    • Water pollution is the addition of external agents that change the composition of a water source.
    • Contaminants include nutrients, pathogens, toxic chemicals, radioactive chemicals, and heat.
    • Industrial, agricultural, and urban runoff cause pollution of lakes, rivers, and coastal waters.
    • Inappropriate wastewater and sewage treatment, climate change, and acid rain can also cause influxes of poisonous chemicals, nutrients, and heat.
    • Nutrient pollution leads to algal blooms and eutrophication, sedimentation fluxes from industrial runoff smother aquatic producer populations, and increasing temperatures stress marine species.


    1. https://www.epa.gov/laws-regulations/summary-clean-water-act
    Frequently Asked Questions about Polluted Water

    What is water pollution? 

    Water pollution is the addition of contaminants to a water source.

    What are the causes of water pollution? 

    The causes of water pollution are:

    • Urban and agricultural runoff,
    • improper sewage and waste treatment,
    • acid rain, and
    • climate change.

    Do nuclear power plants pollute water? 

    Yes, nuclear power plants can pollute water. Pollution of water by nuclear plants happens because nuclear waste is released as discharge, sulphur dioxide and nitrous oxide emissions cause acid rain, and the release of 'cooling water' warms waterways.

    How does urbanization cause water pollution?

    Urbanisation causes water pollution because it produces lots of waste which can pollute waters when improperly disposed of. 

    How to reduce water pollution from factories?

    To reduce water pollution from factories, used water must be treated before being released into water sources.

    Test your knowledge with multiple choice flashcards

    What is water pollution and how can it occur?

    What are the effects of water pollution?

    How is the quality of polluted water scientifically measured and monitored?


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