Crucial determinants of the potential effects of mercury in aquatic ecosystems are the speciation, partitioning, and cycling of its various species. These processes are affected by site-specific factors, such as water chemistry, sediment transport, and hydrodynamics. This study presents two different approaches to the development of one-dimensional/dynamic-deterministic models for the evaluation and prediction of mercury contamination in a lowland tidal river, the River Yare (Norfolk, UK). The models described here were developed to encompass the entire river system and address the mass balance of mercury in a multicompartment system, including tidal reversal and saline limit. The models were focused on river systems, with the River Yare being used as a case study because previous modelling studies have been centred on lakes and wetlands whilst there is a paucity of information for rivers. Initial comparisons with actual measured water parameters (salinity and suspended solids) indicate that both models exhibit good agreement with the actual values.