A major difficulty in the study of macroinvertebrates is the determination for their weight as a measure of the energetic importance of these organisms in an aquatic ecosystem. Therefore, the goal of this study was to find mathematical relationships between the length and biomass of two representative genera of aquatic invertebrates in the Jaboque (Engativa) wetland located in Bogota, Colombia, to facilitate estimation of the mass of individuals. Four surveys were conducted from April 2009 to January 2010. Equations were derived to estimate dry weight from measurements of total body length for the genera Asellus and Helodbella. The length-mass relationships obtained were significant and explained at least 69% of the variance, expressed as the coefficients of correlation (r2= 0.69 and 0.85). These models will allow for the calculation of biomass, and thereby help determine growth and secondary production of these taxa in subsequent laboratory or field studies. In addition, thee equations will help to understand the importance of these organisms to energy flow through consumer pathways in aquatic ecosystems, particularly in urban Andean wetlands, where these organisms are very abundant.