The objective of this paper is to study the hydrochemical characteristics of Lake Dayet Erroumi (Khemisset, Morocco). Three sampling campaigns were carried out in April, July and November 2019. The temperature, pH and electrical conduct-ivity were measured in situ using Hanna Instruments HI 98280. Concentrations of calcium, magnesium, carbonate, bicar-bonate and chloride were analysed by the volumetric method. The atomic absorption technique was used to determine sodium, potassium, nitrate and sulphate. The physico-chemical analysis of the water indicates that the pH is basic. The nitrate and sulphate concentrations show that the water is of good quality according to Moroccan surface water guidelines. Furthermore, the hydrochemical facies of water is of the sodium-chloride type according to the Piper diagram. The value of the electrical conductivity indicates that the lake water has high salinity. The high mineralization of water is explained by the leaching from evaporitic rocks in the region. The principal component analysis shows that the spatial and temporal variation in salinity constitutes the major phenomenon of the hydrochemical characteristics of this lake. Salinity varies inversely with the pH value. The salinity of the water is controlled by abiotic factors (rain and evaporation). However, other parameters (pH, nitrate, carbonate and bicarbonate) depend on biotic factors. Evaporation plays a crucial role in the seasonal variation of the water chemical composition. During wet seasons, the mineralization of water decreases due to dilution by rainwater and the water level of the lake rises (high water period). During dry seasons, lake water evaporates and consequently the mineralization of the water increases, which explains the increase in salinity during the low water period.

The goal of the research was to evaluate the heavy metal detection and potential ecological risks in lake’s water. Geological formations consisting essentially of sandstone and quaternary marine or dune sands characterize the study area. With a climate of the Mediterranean type winters are mild and humid, whereas summers hot and dry. At the analysis center of the Faculty of Sciences, the monitoring of ETMs is carried out by ICP-MS, the processing of data and the validation of the analysis method have been drafted according to the NF T 90-120 standard applicable to the analysis in a laboratory. The analysis covers concentrations of heavy metals, which include Cu, Zn, Mn, Fe, Pb and As, in the water. Pollution load index ( PLI) values were above one (>1) which indicates progressive deterioration of the water quality. However, contamination factor ( CF) values of Pb and Cu, ranging from 8.31 to 15.68 and from 5.5 to 28.05 respectively, show that the studied water remains under a strong impact by Pb and Cu. Considering the severity of the ecological risk ( Er) for a single metal, the descending order of contaminants is Cu > Pb > Mn > Fe > Zn. In relation to the total ecological risk index ( RI), water from the lake shows low to considerable ecological risk.