This paper presents the modeling evolution of fluoride concentration in "river-type" systems. We discuss the fluoride influence on the human body, taking into consideration aspects of fluoride content in drinking water, deficiency and excess fluoride in the body and others. In order to determine the fluoride concentration, we study the problem of mathematical modeling of two-dimensional dispersion of the pollutant. It offers a case study of the Prut River, for which the numerical model of hydrodynamics and the dispersion of fluoride concentration on one sector of the river are applied. The Navier-Stokes equations in differential form Reynolds are used for modeling, as well as the continuity equation and the equation of the pollutants transport. The Surface-water Modeling System (SMS) v. 11.0 was used to develop the numerical models. The results are useful for tracking changes in pollutant concentrations in space and time, in any finite element in the studied river sector (with or without sampling).