MOUHRI1, M. LOUDIKI1 1 Laboratory of Biology and Biotechnology of Microorganisms, Faculty of Sciences Semlalia, University Cadi Ayyad BP 2390, 40000 Marrakesh, Morocco E-mail: samoudisam@gmail.com 2 Laboratory Microorganisms: Genome and Environment, Clermont University, University Blaise Pascal BP 10448, 63000 Clermont Ferrand, France 3 UMR 6023, LMGE, CNRS BP 80026, 63171 Aubiиre Cedex, France 4 UMR5023 LEHNA, University Lyon 1, ENTPE, CNRS, ISARA, University of Lyon, 23 Rue Jean Baldassini 69364 Lyon Cedex 07, France Статья поступила 18.06.15 Принята к печати 11.01.16 ABSTRACT The first results of the horizontal distribution of the cell abundance and toxicity of Microcystis in the hypereutrophic Moroccan reservoir Lalla Takerkoust are reported. <...> An unexpected spatio-temporal heterogeneity has been shown between Microcystis abundance and microcystins concentrations. <...> The horizontal heterogeneity seems to be mainly influenced by the wind direction and inflows. <...> The results can serve as reference data for monitoring cyanobacterial water blooms and associated cyanotoxins in the lake. <...> In Morocco, as in many regions of the world, cyanobacteria toxic blooms have received increasing attention over the last few years due to the potential danger for human and animal health [Jochimsen et al., 1998], and deterioration of drinking water quality [Paerl et al., 2001]. <...> Several studies [Loudiki et al., 2002; Oudra et al., 2002; Sabour et al., 2002] have confirmed the occurrence of toxic cyanobacteria blooms © Samoudi S., Latour D., Robin J., Sabart M., Misson B., Ait Hammou H., Mouhri K., Loudiki M., 2016 673 in different aquatic environments. <...> This work has revealed hepatoxic Microcystis blooms, and characterized microcystins for the first time [Oudra et al., 1998]. <...> While several cyanobacteria species are present in this reservoir, the blooms are mainly dominated by the genus Microcystis [Loudiki et al., 2002]. <...> More recently, [El Ghazali et al., 2011] detected, over a year-long cycle, the presence of microcystins in the lake waters. <...> The concentrations of MC-LR often exceed the WHO norms, particularly during the bloom periods. <...> However <...>