It seems that almost every day there is another story about pollution of one form or another, in the food we eat, the water we drink and the air we breathe. Very often our own actions lead to that pollution and in many cases we can do something about it. These notes explain how you can investigate pollution and advise on positive action to improve our rivers.


Signs of Pollution

If you see dead fish floating on the river or notice that the water is discoloured and smelly any one of the following forms of pollution may be the cause:

  • fertilisers
  • industrial waste
  • oil
  • warm water

All incidents of river pollution should be reported to the Pollution Control officer at the Water Authority giving as much detail as you can: date, time, exact place and precisely what you saw.



If large amounts of fertiliser or farm waste drain into a river the concentration of nitrate and phosphate in the water increases considerably. Algae use these substances to grow and multiply rapidly turning the water green. This massive growth of algae, called eutrophication, leads to pollution. When the algae die they are broken down by the action of the bacteria which quickly multiply, using up all the oxygen in the water which leads to the death of many animals.

Industrial Waste

Chemical waste products from industrial processes are sometimes accidentally discharged into rivers. Examples of such pollutants include cyanide, zinc, lead, copper, cadmin and mercury. These substances may enter the water in such high concentrations that fish and other animals are killed immediately. Sometimes the pollutants enter a food chain and accumulate until they reach toxic levels, eventually killing birds, fish and mammals.

Occasionally poisonous substances are deliberately dumped into rivers and if you see this so-called 'fly-tipping' going on take the registration number of the vehicle and if possible the name of the firm. Report the matter to the police who will then take it further.

Puddle © Dan4th Nicholas CC BY 2.0Oil Pollution

If oil enters a slow-moving river it forms a rainbow-coloured film over the entire surface preventing oxygen from entering the water. On larger stretches of water the oil contaminates the feathers of water birds and when they preen the oil enters the gut and kills them.

Warm Water 

Industry often uses water for cooling processes, sometimes discharging large quantities of warm water back into rivers. Raising the temperature of the water lowers the level of dissolved oxygen and upsets the balance of life in the water.


When sampling polluted water simple precautions must be taken to avoid getting infected. Packed lunches should be eaten before visiting the river or after washing carefully in a supply of clean water. Rubber gloves should be worn and all the equipment should be thoroughly washed at the end of the investigation.

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