The quality of surface water depends on:

The quality of surface water is significantly influenced by numerous factors, as described in the correct choice. The watershed area is crucial because it encompasses all the land that drains into a specific body of water, meaning that any activities within this area can directly affect water quality. Factors such as land use—whether agricultural, industrial, or urban—impact the runoff that enters the water source, potentially introducing pollutants like fertilizers, pesticides, and sediments.

Additionally, the location of the water body matters; for example, a river near urban areas might receive more contaminants than one in a more pristine environment. Sources of pollution can vary widely, including point sources (like wastewater treatment plants) and non-point sources (like agricultural runoff). Lastly, natural agencies of purification, such as wetlands and riparian buffers, play a vital role in improving water quality by filtering pollutants and providing habitats for wildlife.

Understanding these interconnected factors helps in developing effective water management practices and regulations aimed at preserving surface water quality. This multifaceted consideration makes the answer correct as it encompasses the broad range of influences on surface water quality.