What are the causes of water pollution in rivers & lakes and how to check for visual signs of pollution.

River pollution can be caused by:

• Sewage spills – water companies are allowed to discharge (raw, grey water, mixed) sewage during and just after big storms into rivers and lakes. Spills can also be caused by incorrect plumbing in homes & businesses as well as poorly maintained septic tanks.
• Nutrient pollution – naturally, most rivers and streams have a low amount of nutrients like nitrates & phosphate allowing specially adapted wildlife to flourish. When the amount of nutrients increases (mainly caused by pesticides & fertilisers), the water changes resulting in an increased growth of algae, fungi and duckweed. The knock-on effect of this is a loss of light and a change of oxygen levels in water. Because of these changes, naturally occurring wildlife often struggles to survive or in the worst case, completely disappears.
• Industrial and chemical waste – from industrial processes may be (accidentally or purposely) discharged into rivers. Pollutants like cyanide, zinc, lead, copper, cadmium and mercury (to name a few) are absorbed by fish and other animals and then passed down the food chain.
• Warm water – when water is used for cooling processes, large amounts of warm water are discharged, raising the temperature and affecting the natural balance of life in the water.
• Oil – sits like a film on top of the water and prevents oxygen from entering the water. Bad oil spills secially affect the feathers of water birds.
• Microplastics & microfibres, car wax, cooking oils, paint thinners, medications etc, the list of potential pollutants is long – an increasing amount of other chemicals are polluting water bodies; by being washed down the toilet, chucked down the drain or from urban pollution (waste from roads, car wash etc run off into rivers following rain fall and storms).

Sometimes pollution comes from a ‘single’ point, like a tube or pipe. Diffuse pollution tends to come from a large area or over long period of time. This is mostly caused by soil erosion, livestock on river banks, run off from farms, fields, roads as well as from urban areas.

There can be many visual signs to detect pollution. Once these are detected, a laboratory test can provide certainty:

• Sewage related debris, like wipes, sanitary products, tissue paper & cotton buds can be a sign of sewage discharge (causing high amounts of coliform & E.coli bacteria in the water).
• A noticeable odour of sewage, caused by a build up of sulfur-reducing bacteria, often described as a rotten egg smell.
• Sewage fungus is a sign of serious pollution – caused by a build-up of a mass of brown & slimy filamentous bacteria which thrives in nutrient-polluted water. It can often be seen coating stones in the water.
• Algae growth – when a water body is healthy and has little nutrients it is clear and there is little or no growth of algae on the river bottom and on stones. Algae growth, like blue-green algae (cyanobacteria) and potentially a layer of sludge at the bottom is a sign of (regular) pollution which can affect natural wildlife. Specially the presence of cyanobacteria can be harmful to human and animal health.
• Discoloured and smelly water
• Foam, suds on top of the water – foam forms when surfactants are present – some are naturally occurring, but a pure white colour and fragrant smell is a strong sign of pollution.
• Disappearing or reduced wildlife, like dead or gasping fish.
• Oil can often be identified by a rainbow-coloured film on top of the water.
• Variety of wildlife  – when bacteria and other micro-organisms feed on organic matter added to a river, they are using up much of the dissolved oxygen in water (taking it away from natural wildlife). Even a slight drop in oxygen can affect naturally occurring animals:
  • Stone-fly nymphs, mayfly nymphs and freshwater shrimps indicate a high level of dissolved oxygen and are signs for a healthy water body.
  • Other flagship species for healthy water include otters, freshwater pearl mussels and dippers (a short-tailed, plump bird with a low whirring flight).
  • On the other hand tubifex worms and rat-tailed maggots show low levels of dissolved oxygen.

Laboratory Testing:

• Sewage and bacteria can be confirmed by carrying out a lab test for coliform/E.coli and enterococci test (to view all laboratory open water tests please click here).
• Testing for chemical oxygen demand (COD) gives an indication of the amount of dissolved oxygen in water.
• Nutrient pollution can be tested by checking levels of coliform/E.coli, enterococci, ammonia, nitrate and phosphate in water.

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