We studied a sediment core from the lake Khatanga-12 (Taimyr Peninsula, Krasnoyarsk region). The core is 131.5 cm long and covers a period of sedimentation of 7100 years. In this study we made a chironomid analysis and a qualitative reconstruction of paleoecological development of the region and quantitative reconstruction of mean-July air temperature and the water depth in the lake using Russian regional statistical chironomid-based climate-inference models (Nazarova et.al., 2008, 2011, 2015). The lake was formed during the mid-Holocene warming as a result of thermokarst processes. Development of the lake ecosystem Khatanga - 12 in various stages was influenced by climatic factors and cryolitogenic processes. Mid-Holocene warming around 7100 - 6500 calibrated years BP activated thermokarst processes and resulted in formation of the lake basin. Cooling was reconstructed between 6500 and 4500 cal. years BP. The sediments of the lake have been formed by the erosion processes of the lake banks. After 2500 cal. BP reconstructed conditions are close to modern.