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Ground-based measurements of optical properties have rarely been conducted for lakes located on the Tibetan Plateau (TP). In this study, we analyzed the spectral absorption properties of phytoplankton, non-algal particles, and colored dissolved organic matter sampled in Lake Namtso on the TP in order to obtain the variability in the light absorption properties of each of these three components and the relative contribution of each component. The Chlorophyll- a concentration was found to be very low. The mean value of the spectral slope $$S_{280-500}$$ for CDOM absorption was found to be 0.036 nm $$^{-1}$$ , whereas the corresponding mean value for $$S_{350-500}$$ was found to be 0.015 nm $$^{-1}$$ , implying that when comparing spectral slope values with published values, the wavelength range used for deriving them should be considered. Additional peaks were found for phytoplankton sampled in Lake Namtso in the wavelength ranges 310-370 and 600-640 nm, indicating a significant contribution by accessory pigments to the phytoplankton absorption. The Chlorophyll- a specific absorption coefficients of phytoplankton $$[a_{\mathrm{{phy}}}^{*}(\lambda )]$$ at 440 and 675 nm in Lake Namtso were found to be much higher than previously reported values, due to the combination of a small package effect and contributions by accessory pigments. [ABSTRACT FROM AUTHOR]