The exploitation of phosphate mines contributes to the eutrophication of the Foum-Gleita reservoir (Mauritania), leading to the appearance of cyanobacterial blooms. Microcystis aeruginosa and Dolichospermum flos-aquae are the two dominant species during the hot season (May to September), and only the microcystin-LR congener was detected for the first time in a freshwater ecosystem in Mauritania with a peak at 3.55 μg L⁻¹.