This paper is concerned with the simulation of the mixing mechanism of submerged multiport diffusers used to discharge heated water from thermal-electric power plants and households into shallow receiving waters. The three-dimensional turbulence model and hybrid finite analytic method are used to predict the behavior of near field for multiport buoyant jets in rivers. The predicted temperature dilution and velocity prove good by comparison with available laboratory measurements. An empirical formula for temperature dilution and velocity in near field for this kind of flow is given. The effect of parameters on the dilution behavior of multiple jets are also discussed.