The answer is: pesticides.
Eutrophication is a process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a water, leading to increased growth of algae or cyanobacteria.
Fertilizers contain phosphorus and nitrogen, pesticide do not.
NPK ratio system is a conventional shorthand for the ratio of the nitrogen (N), phosphorus (P) and potassium (K) in a fertilizer.
Eutrophication is a serious environmental problem.
