What is a water quality index used for?

A water quality index serves as a valuable tool to summarize various water quality parameters and assess the overall health of a water body. By compiling data about different indicators such as temperature, pH level, dissolved oxygen, and concentrations of pollutants or nutrients, the index provides a concise and comprehensive overview that can be easily understood. This assessment helps inform decisions related to water management, regulation, and potential interventions needed to protect or improve water quality.

In contrast, while increasing agricultural yield, expressing weather patterns, and tracking fishing regulations are all important aspects of water and environmental management, they do not specifically relate to the role of a water quality index. The primary function of the index is focused on evaluating and communicating the condition of water resources, making option C the most fitting choice for the question.