Why would the mouth of a river contain more water than the mouth of one of its tributaries?

The answer to this question is  c. pharmaceutical accumulation  reclaimed water refers to the water that being used again after it already  used for agricultural purposes.this type of water often contains pharmaceutical accumulation because of the chemical fertilizer that is used for the plants is absorbed into the water.

Answer (datum point);

Answer barren with few trees, in the northern hemisphere;