The main effect of the sewage on surface water is its tendency of resulting to water pollution.
A watershed means part of land that contains streams or rivers which links water to a larger body,
When a sewage is been discharged into watershed, its concentration may be diluted but it will gradually diffuse into water bodies and thereby resulting in pollution if there is continued discharge of the sewage.
Therefore, the main effect of the sewage on surface water is its tendency of resulting to water pollution.
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