The water quality control of reservoirs is fundamental since these constitute indispensable renewable water resources for a variety of purposes. A feasible low cost approach that allows for, continuously and globally, monitoring water quality bio-optical quantities was developed through the combination of satellite retrieved water surface spectral reflectance and limnological laboratory analyses. The present approach takes advantage of the Medium Resolution Imaging Spectrometer (MERIS) measurements, onboard ENVISAT satellite, as well as of the in situ samples of chlorophyll a, cyanobacteria and turbidity, regularly collected and analysed. The method is applied to Alqueva reservoir with a surface area of 250 km2, located in the south of Portugal (Alentejo)
