Water quality modeling is crucial for managing water quality worldwide. Different models are available for various environments, but their accuracy depends on the math behind them and the skills of the developer. Factors like data, morphology, and calibration must be considered for a model to be reliable. In Malaysia, these models are extensively used for river rehabilitation and pollution assessment. They help determine the maximum pollution levels that can be tolerated without harming the water quality. Field surveys are also important to account for factors not covered by the models.