The intensification of land uses occurred in recent decades in Uruguay had increased the exportation of nutrients to water bodies, explaining the process of eutrophication observed in this period. Laguna de Rocha is a priority site for biodiversity conservation which belongs to the National System of Protected Areas. However, the lagoon also suffered the impacts of land use changes and has registered some events of cyanobacteria and submerged macrophytes blooms. Strip areas between water bodies and agriculture can function as buffer zones, reducing the nutrient load exported from crops or livestock production systems, providing relevant ecosystem services as maintenance of water quality. With experimental runoff plots we estimated the ecosystem service of nutrients retention, provided by natural grasslands, from a field with artificial pastures. We recorded a 55 % phosphate retention, 44 % dissolved inorganic nitrogen, 28 % suspended solids, 47 % total nitrogen and 42 % total phosphorus.