This paper is an extension of previous work on Celestun Lagoon, Yucatan Peninsula, Mexico, a tropical brackishwater body of 28.1 km super(2) and 14.13 million m super(3). The lagoon system relies upon three main sources of primary productivity, i.e., phytobenthos imports from outside, benthic producers in the system and phytoplankton. The fisheries take 0.061 g m super(-2) year super(-1) from six species of fish and one penaeid shrimp. Based primarily on information from the lagoon, a balanced model of the flows in the ecosystems is constructed using the ECOPATH II software system. As a number of important parameters had to be estimated based on assumed mass balance, the derived model should be considered preliminary. Fish biomass from swept area analyses were found to be too low to meet demands in the system, indicating sampling problems. The value of balanced trophic model for closer examination of data quality is apparent.