Renewable energy resources are now of growing interest and so is the technology to use them. From the available ocean energy resources, salinity gradients are the least studied. The natural coastal processes in countries within the tropics, like Mexico, generously provide the essentials for the development of intense salinity gradients: abundant rainfall and intense solar radiation (high rates of evaporation). A salinity gradient research project at the Mexican Center for Innovation in Renewable Energies of the Ocean aims to quantify and evaluate this natural resource in Mexico, to understand the processes controlling the resource, to characterize the environments at selected sites with potential, to investigate the existing techniques to obtain energy from salinity gradients and to promote new studies to improve the existing technologies. Mexico has numerous rivers discharging to micro-tidal basins and low-inflow coastal lagoons, some of which develop hyper saline conditions during dry seasons. Theoretical estimates of the available energy in one of these sites through one year measurements, revealed higher potential (2-3 times more) than existing estimates at river mouths in the world. Intensive field campaigns are revealing new biological and physical findings together with information providing clues to understand the overall behavior of this delicate and extreme site.