Background/Question/Methods Waterbirds are excellent organisms for investigating links between species and aquatic ecosystem function because they are conspicuous biological components of aquatic systems and often congregate in large flocks. Of the five extant species of flamingos, those restricted to wetlands of the high Andes (Andean flamingo, Phoenicoparrus andinus and James flamingo, P. jamesi) are the rarest, yet the least studied. As dominant primary consumers in shallow Andean lakes and often present in high densities, flamingos may play an important role in the structure and function of their aquatic habitats. Few studies have addressed the influence of flamingos on community structure and ecosystem processes, and none have attempted to link flamingo activities to primary productivity. To explore the influence of flamingos on primary producers, we experimentally excluded P. andinus and P. jamesi from actively used foraging grounds by constructing flamingo exclosure plots (4 m x 4 m) in an alkaline-saline lake in the Bolivian altiplano. To determine flamingo effects on algal biomass and primary productivity, we measured chlorophyll a concentrations and oxygen production in plots from which flamingos had been excluded and control plots to which flamingos had free access. We determined effects of flamingos on algal composition using standard microscopy techniques by comparing algal biovolumes and abundances in exclosure and control plots. Results/Conclusions Plots from which flamingos had been excluded exhibited significantly higher algal biomass than control plots, and also displayed a shift toward large diatom species. Area-specific primary productivity in exclusion plots was lower than control plots, indicating that grazing by flamingos may increase algal turnover rates. These results suggest that, when abundant, P. andinus and P. jamesi can modulate an important ecosystem function, with impacts on community structure. Consequently, high Andes flamingos may exert far-reaching impacts on the structure and functioning and composition of their lake habitats, potentially making them flagships for conservation of high Andes wetlands.