-= Major pollutants found in water =-

Type of pollution:Insecticides, fungicides , weed killers.
Source:Orchards , fields, farms
Effects:Very dangerous as they accumulate (build up)in concentration in all organisms. They are passed on in food chains and can eventually poison the higher animals such as fish , birds and even man.

Type of pollution:Oil
Source:Ships ,factories ,oil terminals
Effects:Blocks the gills of fish.On the surface of still water it prevents the hatchcing of many types of water insects.Cuts down on rate of dissolving of oxygen.

Type of pollution:Synthetic detergents,(washing powder)
Source:Country houses or farms , factories , laundries
Effects:Even in mintue concentrations it decreases rate at which oxygen dissolves.Affects all life which depends on dissolved oxygen.

Type of pollution:Sewage
Source:It is especially harmful in rural areas where the sewage is often dumped in streaams.Pig farms are the major source of stream pollution in the New Territories
Effects:The great increase in plant nutrients cause an explosive growth in algae.Oxygen is used to break down the original sewage and to decompose the algae.The water is deoxygenated to a very low degree.Many natural communities are destroyed.

Type of pollution:Thermal(heat)
Source:Discharge of hot water from factories and especially from power stations or desalination plants.
Effects:Heat accelerates the effects of any other pollutant present.When the supply of heat is constant the whole ecology of the region can change.

Type of pollution:Alkalis, sulphites, chlorine, acids, cyanides
Source:Dyeing and bleaching factories, tanneries, chemical works, canneries, electroplating, metalworks.
Effects:Alters pH of water.Most biochemical system are very sensitive to pH changes.A change of just 1 pH unit can destroy much of the natural life in a stream.Many of these chemicals, especially chlorine, and cyanides are extremely poisonous even in minute concentration.

Type of pollution:Fertilizers.Both night soil and artifical ones such as nitates and phosphates and ammonium compounds.
Source:Agricultural farms
Effects:Similar to sewage.The great increase in plant nutrients cause an explosive growth in algae.Oxygen is used to break down the original sewage and to decompose the algae.The water is deoxygenated to a very low degree.Many natural communities are destroyed.