eng Science and Education Publishing American Journal of Water Resources 2333-4819 2026-01-06 14 1 1 7 10.12691/ajwr-14-1-1 AJWR20261411 article Dogb¨¨ Cl¨¦ment Adjahouinou adjaclem@gmail.com 1 Mouhamadou Nourou Dine Liady 2 Chaim Vivien Doto 3 Richard Adand¨¦ 4 Elias Alexandre S¨¨tondji Adanlokonon 5 Yaovi Zounon 5 6 S¨¨tond¨¦ Baptiste Karen Dossoukp¨¨vi 6 6 Simon Ahouansou Montcho 6 Zacharie Sohou 6 6 Unit¨¦ de Recherche en Aquaculture et Gestion des P¨ºches, Ecole d¡¯Aquaculture, Universit¨¦ Nationale d¡¯Agriculture, Porto-Novo, R¨¦publique du B¨¦nin Laboratoire d¡¯Hydrobiologie et de Recherche sur les Zones Humides, Facult¨¦ des Sciences et Techniques, Universit¨¦ d¡¯Abomey-Calavi, R¨¦publique du B¨¦nin Laboratoire de G¨¦nie?Rural, Ecole de G¨¦nie Rural, Universit¨¦ Nationale d¡¯Agriculture, Porto-Novo, R¨¦publique du B¨¦nin D¨¦partement de Gestion des Ressources Naturelles, Facult¨¦ des Sciences de l¡¯Environnement, Universit¨¦ de N'Z¨¦r¨¦kor¨¦, R¨¦publique de Guin¨¦e. Laboratoire de Recherche en Biochimie et de Toxicologie de l¡¯Environnement, Universit¨¦ d¡¯Abomey-Calavi, R¨¦publique du B¨¦nin This study aimed to evaluate the physicochemical pollution levels in the Cotonou Lagoon, focusing on the dry season, when it receives raw wastewater through various stormwater sewers and drains in the city. Six stations were identified and monthly sampled on the lagoon for this purpose, taking into account the discharge point of the sewers. Temperature, pH, electrical conductivity, dissolved oxygen content, and water transparency of the lagoon waters were measured in situ. Turbidity, suspended solids, and nutrient concentrations, including ammonium, nitrites, nitrates, orthophosphates, and sulfates, of the water samples, were determined using molecular spectrophotometry. Through the assessed physico-chemical, the lagoon waters were found to be nutrient-rich, particularly with ammonium and orthophosphates (up to 10 mg L-1 and 0.5 mg L-1, respectively), detected at levels toxic to aquatic life and indicating early risk of eutrophication, despite the high dissolved oxygen levels recorded. The organic pollution index calculated (varying from 2.67 to 4.33), revealed a heterogenous a moderate organic pollution in most of the lagoon sectors, but a strong and a weak pollution level noticed in other sectors. An effective management of wastewater should be undertaken to significantly reduce the pollution of the lagoon, thereby preventing ecological disasters that may result from eutrophication. https://pubs.sciepub.com/ajwr/14/1/1/ajwr-14-1-1.pdf Aquatic ecosystem estuary pollution eutrophication aquatic biodiversity sanitation