Here's why:

* Runoff: As water flows over land, it picks up various substances like soil, fertilizers, pesticides, animal waste, and industrial chemicals.

* Contamination: These substances can contaminate the water, making it unsafe for drinking, agriculture, or aquatic life.

* Eutrophication: Excess nutrients like nitrates and phosphates from fertilizers can cause algal blooms, leading to oxygen depletion and harming aquatic ecosystems.

* Other pollutants: Other harmful substances like heavy metals, bacteria, and viruses can also enter the water through various sources.

Therefore, the answer is polluted.