Model of nitrification of waste into the Garonne river at the level of the City of Toulouse For several years now the amount of nitrogen in the Garonne, downstream from Toulouse, has been worrying the people managing water supplies. A nitration model is presented, with a law for the growth of the biomass including an inhibition effect, coupled to a hydrodynamic model based on the Saint-Venant equations: the kinetics is propped up with batch experiments, The complete model is validated from observations carried out on the ground. The tool thus made will allow managers to simulate different scenarios and the impact of pollution on the Garonne.