Lake Naivasha Basin is one of Kenya's most valuable freshwater ecosystems, supporting rich biodiversity, fisheries, horticulture, tourism, geothermal development and domestic water supply. Despite its ecological and socio- economic importance, the basin is increasingly threatened by pollution, excessive water abstraction, catchment degradation and sedimentation. To assess the health of the basin, the Kenya Marine and Fisheries Research Institute (KMFRI) conducted a comprehensive assessment between 2024 and
2026. The study covered the three main inflowing rivers, Malewa, Gilgil and Turasha, as well as Lake Naivasha itself. Water quality, nutrient concentrations, microbial contamination, phytoplankton, zooplankton and macro-benthic invertebrates were analysed across nine river sampling sites and eight lake sampling sites to determine the current pollution status and ecological condition of the basin.