Through monthly evaluations, the main species of fish captured by the fisherman of Lagoa Pequena, a site in the estuarine region of Lagoa dos Patos – RS, were identified. The biomass data, in addition to the absolute and relative frequencies of each species, were submitted to correlation analysis with the seasons of the year and environmental variables. Although water salinity was found to be constantly above 3.5, there was a predominance of the capture of 85.8% of characteristic freshwater species and 15.5% of estuarine species. The economic values of the species, the types of fishing and the seasons of the year are the main determinants of the local fishing production.