Abstract: Increasing shrinkage and salinization is occurring in China's inland lakes. Lake Chenghai is located in the southwestern plateau of China and it is one of only three lakes in the world where Spirulina is found naturally, which has experienced severe decline in water level in recent decades (especially between 2006 and 2016). In addition, in China, there is a lack of hydrological observation data collected for many of the similar plateau inland lakes, which has led to a research gap regarding water-salt balance. This study aimed to investigate the lake water-salt balance, identify the causes for the decline in water volume and the adverse effects of the transition of a freshwater lake to a saline lake. A coupled water-salt balance mathematical model of the lake was constructed to gain insight into inland water-salt variation in this data scarce region. For Lake Chenghai, there was a 6.43 m decline in water level with an average rate of decrease of 7.0?cm?a?1 between 1970 and 2016; the multi-year average water shortage was 2945?×?104?m3?a?1 from 2006 to 2016. The variation in the water level was positively correlated with precipitation (R?=?0.81, P?
（1）The warm and dry climate is the main reason for the Lake Chenghai shrinkage.
（2）A coupled water and salt balance model is available for data-scarce regions.
（3）Water volume and salinity changes affect the phytoplankton and pH in Lake Chenghai.
（该篇论文发表于《Science of The Total Environment》，作者为水环境研究所2016级博士生）