(Transcription of audio on video)
Water can be polluted from many sources. Faecal contamination from sewage makes water unpleasant and unsafe for recreational activities such as swimming, boating or fishing.
Many organic pollutants, including sewage effluent and farm and food-processing wastes consume oxygen, suffocating fish and other aquatic life. Nutrients such as nitrates and phosphates, from everything from farm fertilisers to household detergents, can 'overfertilise' the water causing the growth of large mats of algae, some of which are directly toxic. When the algae die, they sink to the water bottom, decomposing, consuming oxygen and damaging ecosystems.
Chemical contaminants including heavy metals, pesticides and some industrial chemicals can threaten wildlife and human health.
Sediment run-off from the land can make water muddy, blocking sunlight and, as a result, killing wildlife.
And irrigation, especially when used improperly, can bring flows of salts, nutrients and other pollutants from soils into water.
Source: SOER 2005