To simulate the concentrations of dissolved inorganic phosphorous (DIP) of a tropical coastal lagoon, ?Ci?naga Grande de Santa Marta? (Caribbean, Colombia), the largest and most important coastal lagoon complex in Colombia, we developed a dynamic model with a program language STELLATM. The model is parameterized based on sixteen years of experimental data belonging to different authors and entities request to information register about the rainfall, evaporation, flow and DIP concentration variables at all sources and sinks of the lagoon. Two time periods separated data series due to additional source of water and DIP from ca?os Clar?n, Aguas Negras y Renegado, which arrive from Magdalena River to obtain two sub-models. Calibration of the model yields a good fit of predicted to observed lagoon volume and DIP concentration inside the standard deviation of empirical data from center of lagoon site. Validation showed the effects of hydrology, sedimentation and resuspension on the DIP dynamics including the wind and dissolved oxygen.