Fertilizers are plant nutrients used to supplement nutrients already available in the soil and to enhance the growth of the plants being cultivated. The indiscriminate use of fertilizers near water bodies leads to what is called "eutrophication." The results of excess nutrients in the water bodies can cause a lot of damage. These include the growth of phytoplankton, algae and other microbes. The rapid growth can trigger a sudden increase in substances that are toxic for other organisms living in the water body. Fertilizers can be harmful for native species of the water body and enhance the growth of unwanted organisms. Many instances of large scale death of fish has been noticed when fertilizers are introduced into water bodies.
Similarly, herbicides are compounds that are intended to kill unwanted plants which use up nutrients meant for the crops being cultivated. In water bodies, herbicides target the natural plant species and lead to their death. This destroys the food sources of many animals and can severely reduce the oxygen content of the water causing the death of many organisms living in the water body.
These factors make it essential to ensure that fertilizers and herbicides are used in a controlled manner on crops especially near water bodies.