Macro- and microalgae have recently received much attention due to their valuable chemical constituents. In order to increase existing data, the authors studied nineteen microalgae species isolated from different reservoirs in the Fez region (northern Morocco), undertaking experiments to determine for each species the specific growth rate, their total amounts of proteins, carbohydrates and lipids and the influence of the growth phase on these chemical constituents. The growth rates of the nineteen studied species of microalgae showed a wide interspecies variation, ranging from 0.27 d-1 for Chlamydomonas nivalis to 3.64 d-1 for Chlorococcum wemmeri. Protein, carbohydrate and lipid contents also varied greatly between taxa and within genera. Ankistrodesmus falcatus, Chlamydomonas nivalis, Chlorococcum sp., Fragilaria ulna, Scenedesmus protuberans, and Synechocystis aquatilis tended to synthesize proteins, the concentrations exceeding 20% of dry weight (DW). Ankistrodesmus falcatus, Ankistrodesmus sp., Chlorococcum wemmeri, Coenocystis sp., Isocystis sp., Lyngbya bergei, Oscillatoria amphibia, Polytoma papillatum, Scenedesmus protuberans, Scenedesmus sp. and Synechocystis aquatilis showed a high capacity for lipid storage, higher than 20% DW. For carbohydrate contents, only Scenedesmus protuberans and Scenedesmus quadricauda showed an excessive level, compared to other scanned species with 29.21% and 24.76% DW, respectively. Green algae, Scenedesmus protuberans for example, generally tend to synthesize proteins, with a content reaching 45% DW, while blue-green algae, for example Lyngbya bergei, tend to synthesize lipids, with a content reaching 50% DW.