From Saline to Freshwater: Ecological Shifts, Emerging Fisheries, and Health Risks in Lake Nakuru

ABSTRACT Lake Nakuru, historically a hypersaline lake in Kenya's Rift Valley, has undergone a significant ecological transformation due to a sustained saline–freshwater inversion driven by increased rainfall, catchment degradation, and anthropogenic inputs. This study provides a spatially resolved assessment of the lake's current physico‐chemical status, biological structure, and socioeconomic dynamics. Results show a dramatic decline in salinity from historical levels of 20–40 to 2.58–2.6 g/kg, weakening the lake's buffering capacity and altering nutrient stoichiometry. Molar TN/TP ratios across all sites were exceptionally low (0.09–0.19), indicating persistent nitrogen limitation and conditions conducive to cyanobacterial dominance. Microcystis comprised 27.58% ± 3.78% of the mean dietary contribution of Oreochromis niloticus , whose proliferation reflects a major shift in the lake's food web. Flamingo populations have declined, likely due to the collapse of their specialized food base. Microbial contamination was highest at river inflow sites. Further, we found elevated concentrations of arsenic and lead in fish tissue, raising critical public health concerns. The emergence of an informal tilapia fishery, driven by ecological changes and declining tourism, has introduced new economic opportunities but also sparked conflict due to its illegality within the protected national park. Vulnerable groups, particularly women, face heightened exposure to both economic instability and health risks. The findings indicate that Lake Nakuru has moved beyond early pollution symptoms into a phase of advanced ecological disruption, underscoring the need for urgent, multisectoral interventions.