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Dayat Roumi Lake, a vast body of permanent and shallow water in Morocco, is exposed to urban, tourist, and agricultural constraints. This human intervention can lead to microbial pollution of the lake ecosystem, hence the need to assess this contamination. For this reason, we undertook in this study an evaluation of the microbiological quality of the lake's water. Thus, seasonal water samples were taken at eight selected stations, taking into account the reception sites of the tributaries and anthropic activities. The parameters determined were: temperature (T), pH, dissolved oxygen (DO), electrical conductivity (EC), biological oxygen demand (BOD), chemical oxygen demand (COD), ammonium (NH4+), nitrates (NO3-), orthophosphates (OP), total phosphate (TP), total coliforms (TC), fecal coliforms (FC) and fecal streptococci (FS). The results reveal: - A high water conductivity exceeding the admissible value recommended by the Moroccan standard. - A significant presence of coliforms and fecal streptococci, in dry periods, exceeding the standards set by the WHO, which could be attributed to a summer temperature favorable to the development of coliforms. This fecal contamination leads to an increased consumption of dissolved oxygen (high BOD and low DO values) explaining the fish mortality in this period of the year. - The principal component analysis identified the sources of water quality degradation as domestic sewage, agricultural run-off, domestic waste, and human and animal excreta. - The hierarchical analysis divided the sampling stations into three different clusters. The results of the MQI classified the waters from not to highly polluted. Station 4 was classified as the most polluted site. The results of the DOC/BOD ratio showed a spatial and temporal heterogeneity of the biodegradability of the oxidizable matter present in the lake waters. For all these reasons, an effective management plan must be established to protect this water body from further pollution.