A chlorophyll (Chl) a retrieval algorithm, originally developed for spectral subsurface irradiance reflectance determined from above-water shipboard measurements, was adapted for use with satellite imagery to be acquired by the MERIS (Medium Resolution Imaging Spectrometer) instrument. This MERIS algorithm was calibrated for Chl a concentrations in the range 3–185 mg m-3 using spectral reflectance calculated from shipboard measurements on the IJssel Lagoon (The Netherlands). Next, the algorithm was validated for various inland and coastal waters covering this concentration range. Despite the lower spectral resolution of MERIS as compared to the shipboard spectroradiometer, the standard error of estimate is expected to be similar, i.e. 9 mg m-3 of Chl a in mesotrophic and eutrophic lakes, rivers, estuaries and coastal waters.