The objective of this study was to evaluate the typology of water through physicochemical and bacteriological characterization with the aim of highlighting its vulnerability as a drinking water resource. The methodology adopted was to evaluate the level of pollution by monitoring the spatiotemporal variation of the water pollution indicator levels of Lake Dohou. The sampling frequency is monthly for one year, from November 2017 to October 2018, in order to obtain a fairly representative image of water quality and its seasonal evolution in eight (8) well-defined stations. The parameters were determined using the standard methods defined by the French Association for Standardization (AFNOR). This study shows that the waters are acidic, with an average pH of 5.81 and a low electrical conductivity of between 42.67 ± 4.30 and 59.62 ± 21.84 μS•cm −1. At all stations, seasonal mean water transparencies are low (<1 m). It is also noted that 99.7% of the water samples collected had total nitrogen (TN) levels above the limit of 4 mg•L −1. All of the lake's waters have non-compliant BOD5 (<3 mgO 2 •L −1) for raw water intended for the production of drinking water. Sites D6 and D7 have COD/BOD5 ratio greater than 3, which indicates the presence of non-biodegradable organic matter in these areas. Total coliforms, Escherichia coli and Enterococci were present in 100% (28/28) water samples at concentrations ranging from 2300 to 173,000 CFU/100 mL, from 100 to 1650 CFU/100 mL and from 20 to 1140 CFU 1/100 mL respectively. For Salmonella pathogens, they were detected in 50% of the dry season samples and in 100% of the rainy season samples. This almost permanent presence of this pathogenic germ denotes a poor quality of water with reference to this parameter.

The conservation status and the vulnerability to fishing pressure of the ichthyological population of the Bandama River located in the Marahoué Region (Côte d'Ivoire) were assessed. Sampling of fish fauna was conducted from September 2019 to November 2020 using experimental and artisanal fisheries. The results of International Union for Conservation of Nature show that, the majority of the fish species (88.7%) inventoried were classified as "least concern". The "high to very high" and "very high" categories are represented respectively by two species and one species. These include Heterobranchus longifilis and Malapterurus electricus, which belong to the "high to very high" vulnerability category, and Clarias gariepinus, which belongs to the "very high" category. In addition, 79.87% of the species in this stand have vulnerability between "low" and "moderate".

The purpose of this study was to evaluate the contamination by heavy metals and the health risks of the residents of a watershed of the Sassandra river. Water and fish samples were taken from Guessabo Lake during the dry season and the rainy season. The average Hg, Pb, Cd and Zn concentrations in the water samples decreased during the rainy season by 20.51%, 80%, 18, 26% and 61.4%, respectively. In contrast, the average concentrations of As, Cu, Mn and Fe increased by 10%, 84.3%, 48.98% and 11.45%, respectively. The concentrations of heavy metals in water samples follow the trend: Fe> Cu> Mn> Pb> As> Zn> Hg> Cd. All metals except Fe were within permitted limits for drinking water quality at all stations during both seasons. The increase of As, Mn and Fe in water samples during rainy season was inversely proportional to their covalent index. The average heavy metal pollution index (HPI) for each sampling station showed higher pollution at the G2 station. The average Heavy metal evaluation index (HEI) of dry season (28) decreased relatively after the rainy season (21). Pearson's analysis showed that cadmium correlates strongly with HPI (r = 0.896) and HEI (r = 0.95) and iron is also highly correlated with HPI (r = 0.961) and HEI (r = 0.999). The concentration of trace metals obtained in the muscles of Chrysichthys nigrodigitatus (demersal) and Tilapia spp (benthopelagic) showed that Tilapia spp concentrated more non-essential metals (Hg, Cd and As) than Chrysichthys nigrodigitatus. Human health risks of trace metals in fish muscle and water were low, but among the selected metals, As and Hg are the non-essential elements contributing more to the cumulative hazard quotient of HI (0.845) for children and (0.39) for adults.

The objective is to study the phytoplankton community of Dohou Lake in order to contribute to the knowledge of its ecological quality. For this purpose, monthly samplings were carried out annually between October 2017 and September 2018. The studied physicochemical parameters (Temperature, Electrical conductivity, pH, Dissolved oxygen, Transparency, Depth, Total nitrogen, Nitrate, Nitrite, Total phosphorus) varied significantly over time. During the rainy season months, Dohou Lake is influenced by high values of total phosphorus, total nitrogen, conductivity, nitrate, pH, transparency and depth. However, in the dry season, the lake is characterized by high values of temperature, nitrite, dissolved oxygen and conductivity. For the phytoplankton community, 373 phytoplankton taxa divided into 111 genera, 51 families, 24 orders, 11 classes and 7 phyla (Chlorophyta, Euglenophyta, Cyanobacteria, Bacillariophyta, Pyrrophyta, Chrysophyta and Xanthophyta) have been identified. Chlorophyta with 50.67% is the most represented in the taxonomic richness of the environment. Total phytoplankton densities oscillate between 100 105 cells / L (August) and 321 105 cells / L (February) with high proportions of Cyanobacteria greater than 45% during each month of the rainy season. The highest values of Shannon and Equitability diversities are observed during the dry season months.

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