The spectral library approach requires a quantification of the range of signatures expected for any species under natural conditions.14–17 In nature, however, there exists a considerable variation in pigment composition and quantity among broad taxonomic groups and even within species. For example, the brown algae may range in color from beige to almost black.18 Such differences may be related to species-specific character of pigment composition but also induced by environmental factors, such as light, nutrients, and water flow.10 Moreover, the overall spectral appearance of an alga cannot necessarily be inferred based only on the knowledge of the pigments present. The morphology, thickness of thalli, and cellular architecture affect the relationship between pigment densities and absorption spectra19–21 and, consequently, affect the formation of reflectance spectrum. At the other extreme, however, some authors have questioned whether spectral signatures of individual plants are unique at all.15 This plethora of diversity makes it very challenging to establish the typical ranges of reflectance spectra of macrophyte species and assess significant differences among groups. To date, spectral signatures of the ecological end-members have been published for some corals, macroalgae, and seagrasses.9,18,22,23–25 Nevertheless, these studies mainly concentrated on species growing in ocean waters. Moreover, very few did account for the variability of spectral signal within and between species (e.g., 22). To assess a potential of remote sensing methods for monitoring macrophyte beds, however, ranges of spectral signal of macrophyte need to be quantified, and spectral regions that consistently allow discrimination of species or taxa need to be defined.