The Tolka River and Estuary, Co. Dublin, Ireland, is a typical Irish urban river and estuarine system. It has significant metal and organometal contaminant loading. A one-month rapid sampling and analysis regime was devised to optimise riverine and estuarine sampling techniques and to determine seasonality of contaminant distribution. Over a thirty-month period contaminant concentrations within the surface sediment of the aquatic system were analysed from twenty sampling points. Six metals (Cd, Cr, Cu, Ni, Pb and Zn) and an organometal (TBT) were analysed using Differential Pulse Polarography for thirty and nineteen months respectively. Organic Matter, Suspended Particulate Matter, pH, Salinity and metal content of the water column were also analysed. This thirty-month assessment created an extensive database to determine spatial and seasonal distributions of contaminants over time and various in situ environmental and anthropogenic parameters that influence these distributions. It was found that contaminant concentrations within surface sediment are highly variable over a twelve-month period and that environmental conditions and anthropogenic sources of contaminants are the key factors affecting spatial and seasonal distributions.