This paper studies the dynamics of organic matter and pollutant load in the most impacted the Frio river located south west of Santander Department. The modeling conditions to minimize the calibration error of parametric variables that support the degradation of the organic load. Hidrogeometrico system information, dissolved oxygen, carbon, nitrogen, pathogens, and weather variables necessary for modeling. The parametric error is calculated using the Monte Carlo algorithm and the likelihood of widespread uncertainty, GLUE, (Generalized Likelihood Uncertainty Estimation). Rates kinetic or parameters display a coeffi cient of determination (R2) average of 0.88 and 0.92 for variables. The simulation study shows how 61.9 ton.d-1 organic load discharged by 38,3000 people in Floridablanca and Bucaramanga, accumulate in the river 16.85 ton.d-1 changes generating in the balance of dissolved oxygen as a result of increased carbon and organic nitrogen.