An improved understanding of water quality issues in specific basins is required to assess how the benefits from often costly interventions contribute to the overall basin water quality. Water quality assessment is the evaluation of the physical, chemical, and biological condition of a water resource in relation to intended uses. It encompasses monitoring, data evaluation, reporting, and dissemination of the condition of the aquatic environment.

The design of a monitoring network involves selecting the monitoring sites, the monitoring frequency, and the parameters that best demonstrate the water quality issues being managed. Samples can be taken either from the water, from suspended matter in the water body, from sediments at the bottom, or from organisms in the water or sediments.

Processing and interpretation of water quality data is a critical step to define water quality management plans. A good plan should include actions to be undertaken, responsibilities for ensuring implementation, and a time schedule.