The 7 ways in which we can pollute water

Physical impacts

For many years in the UK people culverted, dammed, straightened and generally controlled rivers.  We did this mostly to prevent flooding or because water and the riverine environment have simply got in our way or been developed.  The extensive areas of hard standing in our cities, roads and the wider urban environment create unnatural flow conditions in rivers and streams. Rainwater drains away faster than it would normally because it can't soak into ground to recharge rivers in drier weather.  In some situations this causes flooding.

Often in the past, human intervention hasn't been sensitive to the environment or the creatures that live in and around rivers and coastal areas.  In many places we're now changing the way we manage rivers and coastal areas by working with nature rather than against it.  In some cities we're even starting to open up rivers and take them out of culverts so they form an attractive feature for people to enjoy.

Other sorts of physical impact include the input of heat or silt.  One of the more significant impacts can be from power stations that discharge cooling water at higher than normal temperatures.  Human activities can also cause pollution when silt and inert solids enter rivers and seas from agriculture, quarrying and construction sites.

Biological impacts

Humans affect the environment and its’ use through ‘biological impacts’.  These include the introduction of alien species such as invasive plants like Himalayan balsam or creatures like mink or signal crayfish that dominate over native species.

Other biological impacts include pathogens or disease agents that harm the environment or its’ use in some way.  Pathogens such as harmful bacteria and viruses usually come from sewage inputs but there are other sources such as diseased fish, farm animals or introduced species. 

In the UK we're particularly interested in pathogens when affect bathing water standards because that presents a health risk for people swimming in the sea. 


Toxins affect the water environment and things that live in it in one of two ways.  They cause either acute [immediate] effects or chronic effects that build up over a longer time period. Examples of acute toxins might be ammonia from the breakdown of sewage and other organic material.  Many substances also have acute effects if they are present in high doses. Chronic toxins are those substances that ‘bio-accumulate’ or are persistent in the environment.  Examples include heavy metals like mercury or lead, pesticides and even hormones from the birth control pill. 

For many people the thought of unknown chemicals or toxins, even in small quantities, in our water, rivers and streams is a matter of concern.  But it's important to understand how toxins affect the environment and the current risks and science.  Over the last century, our society has used more and more chemicals which have many benefits and have transformed our lives.  We now understand far better how many of these substances affect us and the environment and we have adopted a more precautionary approach.  In many cases we've banned or phased out the use of certain substances or controlled their use far more carefully.  But for some substances, our knowledge of the impacts is still emerging and there are some significant ‘legacy’ issues that remain.  More information on the chemicals of concern found in misconnections can be found in the previous section.


Oxygen dissolves readily into water but not in great quantities and less as temperature increases.  Fish and other creatures that live in rivers need dissolved oxygen.  When we introduce certain substances [pollutants] into water they break down and in doing so remove the oxygen.  If there's no dissolved oxygen fish and other creatures can't survive. 

Many pollutants that this effect – sewage, milk, farm slurry, foodstuffs.  When plants and algae breakdown they can also remove oxygen from water. For most UK rivers, dissolved oxygen levels have improved significantly over the last 20 years.


Eutrophication is the term used to describe the introduction of nutrients into water to enrich it and they cause adverse impacts. Nutrients are essential for growth but rivers, lakes and streams are very sensitive to any changes from normal levels.  Nutrients act as a fertilizer easily changing the types of plants and ecology in a water body.  Where there is eutrophication this often leads to the growth of algae that smothers other plants.  When this algea dies back in autumn and winter it reduces oxygen levels. 


The introduction of radioactive isotopes is a rare type of pollution and can be either from nuclear activity or natural sources. Radioactive isotopes are used for many purposes: defence, power generation, research, medical and commercial uses.  Such uses are tightly regulated by the Environment Agency but other radiological sources are naturally occurring such as radon gas venting from rocks and getting into groundwater.


Many of the UKs’ rivers and beaches are beautiful and wild places.  They are unique environments and a source of enjoyment and recreation for many people.  In some places, due to neglect, past engineering, litter and other visual impacts their appearance is not as it could or should be.  Litter is a particular problem in urban areas as it washes off roads and hard standing areas into surface water sewers that ultimately end up in rivers or the sea. Other significant aesthetic impacts come from things like road run off containing oils and silt. 

All these types of pollution can have cumulative impacts on rivers, lakes and seas