What is the main source of pollutants entering waterways?

The correct answer highlights that pollutants entering waterways can originate from multiple sources, including agricultural runoff, sewage discharge, and industrial waste. Each of these sources contributes significantly to water pollution in different ways.

Agricultural runoff, which includes fertilizers, pesticides, and other chemicals used in farming, can wash into rivers and lakes during rainfall. This runoff can lead to eutrophication, harming aquatic life.

Sewage discharge introduces pathogens, nutrients, and organic matter into water systems. This can degrade water quality and pose health risks to humans and wildlife.

Industrial waste can include heavy metals, toxins, and other hazardous materials, which can have severe impacts on aquatic ecosystems and human health when they contaminate waterways.

The presence of multiple sources reinforces the complexity of water pollution and the importance of addressing all of them to achieve cleaner water environments. Thus, the most comprehensive choice recognizes that all listed options are significant contributors to pollutant levels in waterways.