Ogii Lake is a freshwater lake located in the eastern Arkhangai province, central Mongolia, which registered as an International Ramsar Convention site in 1998. This study sought to estimate the environmental characteristics of Ogii Lake and Orkhon Valley. The authors analyzed water samples from springs, streams, the lake, and groundwater in the summer of 2017 and 2018. A questionnaire survey was undertaken in August 2018 to evaluate anthropogenic impacts on the lake’s environment. In this paper, we present two years of water analysis results, the potential waste generation derived from livestock and tourists around the lake, the normalized difference vegetation index (NDVI) surrounding the lake, and the surface area changes of Ogii Lake in the past decades. The physicochemical parameters of water samples were analyzed using the standard methods that are recommended by the American Public Health Association. Our study confirmed that the water quality of both Ogii Lake and Old Orkhon River was classified as clean; however, PO43- concentrations were determined 2.7–3.4 times higher than the standard level in 2018. The observed high PO43- concentration might have been attributable to livestock distribution around the lake in spatially and increasing discharge after summer intense precipitation in temporally.
