The last cause is pesticide residues from agriculture. We should cut used to pesticides residues from agriculture as much as possible to drop toxins from the used to chemicals in agriculture. The chemical was leaching into the ground water. Usually flow through the soil into the river. According to Abdul Azeem said that "Pesticides that get applied to farm fields and roadside and homeowners' lawns run off into local streams and rivers or drain down into groundwater, contaminating the fresh water that fish swim in and the water we humans drink."(p.3).