Correct Answer - Option 3 : Rivers
Concept-
If a large amount of suspended matter such as clay, silt or some other finely divided organic materials is present in water, it will appear to be muddy or cloudy or turbid in appearance. The turbidity depends upon the finesse and concentration of particles present in water.
Although, the clay or other inert suspended particles may not be harmful to health, yet they are to be removed or reduced for aesthetic and psychological reasons.
The turbidity is measured by a turbidity rod or by a turbid meter with optical observations, and is expressed as the amount of suspended matter in mg/l or ppm.
The standard unit is that which is produced by 1 mg of finely divided silica in 1 l of distilled water. A turbidity in excess of 5 units is easily detectable in a glass of water, and is thus, usually objectionable. Turbidity in clear lake water is about 25 units; and for muddy waters, it exceeds about 100 units.
In oceans due to turbulence the suspended impurities come to the shore and in case of lakes and wells they settle. But rivers have high turbidity in comparison to other sources of water.
