We present the results of dispersion simulations of faecal coliform bacteria in the coast off Puerto Escondido, Oaxaca, Mexico. To perform the simulations we used the software 4.9 Mohid, from Technical University of Lisbon, Portugal. The inputs for the software were bathymetry, wind direction and speed, sewage discharge, faecal coliform bacteria concentration at the point of discharge, salinity, temperature and dissolved oxygen in coastal waters. The output was the distribution pattern of pollutants. The path of pollutants allowed to determine the most affected area in different weather conditions and the amouht of tourism present in the area.