Mercury in aquatic ecosystem is of great concern due to its toxicity,bioaccumulation and magnification in food web.The Tibetan Plateau(TP)is endowed with the highest and largest lakes on earth,whereas Hg speciation and distribution in lake waters are least known.In this study,surface and vertical water samples from 37 lakes over the TP were sampled and determined for the total mercury(THg)concentrations.Results showed a wide range of THg concentrations from < 0.5 and 37.11 g/L,with dissolved Hg as the dominant speciation.THg concentrations in lake waters exhibited an increasing trend along the southeast to northwest transect over the TP.Strong positive correlations were found between THg concentrations and salinity and salinity-related environmental variables,especially for total dissolved solids(TDS)and the dominant soluble ions such as Na+,K+,and Cl-1.Vertical distribution of Hg in lake waters does not show clear variation.The large-scale geographical pattern of climatic and environmental factors leads a decreasing precipitation and an increasing evaporation northwards and westwards,resulting in gradient enhanced enrichment of soluble substances in lake waters,which are able to complexe more Hg.Our study highlights the concurrent Hg and salinity in lake waters and the natural control the spatial distribution of lake water chemistry over the TP.The results are potentially valuable in understanding the mercury biogeochemical cycling over the TP and perhaps high-altitude regions beyond.