Assertion: Fertilizers are an important source of water pollution.
Reasoning: They are washed down to rivers, lakes and tanks & induce an increase in the nitrate content of surface waters.

Both Assertion (A) and reasoning (R) are correct and R is the correct explanation of A.

Various types of chemicals used in modern agriculture such as inorganic fertilisers, pesticides and herbicides are also pollution generating components. These chemicals are washed down to rivers, lakes and tanks. These chemicals also infiltrate the soil to reach the ground water. Fertiliser induces an increase in the nitrate content of surface waters.