The quality of the water in terms of its chemical composition determines its viability to sustain life and end uses. The ability to model water quality in rivers and lakes is not an easy task as this involves both the hydrology of the catchment but also land management, geology and biological processes that add or remove chemicals as the water moves through and over the soils. Point sources from industries and municipalities are also sources of chemical input to rivers and lakes. Models to predict the chemical composition of the water in rivers and lakes is vital to assist with management and understanding. These models can vary from mechanistic to statistically based. We invite authors to submit papers on such models to this session.