This study investigates the environmental impacts of sand dams on biodiversity and ecosystem services along the Kikuu River in Makueni County, Kenya, an arid and semi arid region where water scarcity and food insecurity remain critical challenges. While sand dams are widely promoted as sustainable water management interventions, their ecological effects on biodiversity and ecosystem services are less documented compared to their hydrological benefits. Addressing this knowledge gap, the study aimed to evaluate how sand dam construction influences plant and animal diversity as well as the provision of ecosystem services in the Kikuu River system. The research was carried out between 2023 and 2024 and covered a 35 km stretch of the Kikuu River, where 21 sand dams were identified. A total of 306 households were sampled. Data collection involved mapping natural (e.g., Acacia species, xerophytic grasses) and human-made features (e.g., water pumps, roads), biodiversity surveys of plants and animals in both sand dam and control sites, and household interviews on ecosystem services. Sampling methods included perpendicular transects, spot checks, and sweep counts. Data were analyzed using Welch’s ANOVAwith Games-Howell post-hoc tests, Pearson Chi-square tests, and regression analyses. The results indicated that sand dam sites supported higher plant and animal biodiversity compared to control sites without dams (p < 0.001). For instance, the Kwa Moses and Mbukoni dams demonstrated rich vegetation cover and increased animal presence, while regression analysis revealed that sand dams had a positive and significant relationship with ecosystem service ratings, particularly in water provision, irrigation, and soil stability. However, variations in performance among dams highlight the influence of design, location, and maintenance. The study concludes that sand dams significantly enhance biodiversity and ecosystem services in semi-arid landscapes but require site-specific management strategies, continuous monitoring, and design improvements to maximize benefits and reduce ecological trade-offs. It recommends the strategic expansion of sand dams, coupled with community participation and post construction monitoring, to strengthen ecological resilience and sustainable development in water-scarce regions