Abstarct: Rivers as one of the sources of surface water receive wastewater from human activities and with the help of the advection-diffusion process, they dilute pollution on river path and reduce the density. This property, which is known as self-attenuation, enables the release of the contaminated wastewater into the rivers while the average water quality in the river remains acceptable for various purposes. The dilution process takes a minimum distance which depends on the contaminant concentration and entrance position as well as hydraulic conditions such as velocity and angle of attacks. Reduction of this length is of engineering interests since the region of high concentration pollution is confined. Therefore by increasing turbulence in water, the mixing length will be decreased. A method to increase the turbulence is to use spur dikes. In this investigation, the numerical simulation of the flow is done by the Flow-3D software in a rectangular channel. There are three main parts in this study including: the flow without taking into consideration pollution. The flow streams resulting from simulation was totally in accordance with experimental data. The second main part was to simulate the flow by taking into consideration pollutant entrance. The third and the most important one, was to study the effect of geometrical characteristics of spur dike and flow rate change. To do so, spur dikes of length 0.1 to 0.7 meter have been used. Finally, the effects of different points of pollutant entrance and depth parameter on the pollution dispersion has been discussed. The LES turbulence model is used in this investigation. The results show that, changes made in the location of pollution source and spur dike, heavily affect pollutant release Such that by locating pollution in the center of the eddy, and pollution entrance from channel tray, the best results have been achieved.