There is devoted to the comprehensive analysis of studies of one of the oldest estuaries of North-West Black Sea — the hyperhaline Kuyalnyk Estuary (an analogue of the Dead Sea in Ukraine). The interest for its study is determined by the richness of its mineral and balneological resources. The special attention attracts the valuable sulphide muds, which value, according to preliminary estimates, is about 7 billion dollars. Currently estuary is suffering from an ecological disaster: it is drying up, its morphometric characteristics are changing catastrophically (the water area surface and the depth are decreasing), the brine mineralization reaches 300 ‰ or more, and the salt from the exposed bottom of the estuary is transported to considerable distances, which threatens the salinization of agricultural lands and homesteads of coastal settlements. In that conditions the estuary loses the ability to restore its invaluable natural resources. Comprehensive information on the assessment of Kuyalnyk Estuary state and the state of its resources is extremely important for the development of measures for protection, restoration and preservation of this unique treasury of natural resources and the implementation of strategy for their rational use. We carried out a critical analysis and generalization of Kuyalnyk Estuary geoecosystem research results for the over a nearly 200-year period (1829-2020) for the first time. Here are highlighted the main stages and reflected directions of research, presented their chronology. The research and publishing activities also highlighted. The role and the work of societies members which were created at the Imperial Novorossiysk University (now the Odesa National University named after I.I. Mechnikov) in direction of research into the nature of Odesa estuaries, and in particular Kuyalnyk Estuary, its mineral and balneological resources, are discussed. The contribution of scientific organizations and scientists to development of research on the current stage also analyzed. The main attention paid to the fundamental complex research of the geo-ecosystem of Kuyalnyk Estuary. It shown that the modern period characterized by quite powerful system of data collection and intensive accumulation of knowledge about this unique reservoir. This made possible to generalize the material accumulated over these two centuries, which reflected in the work started in 2018. "Encyclopedia of Kuyalnik estuary" (in 8 volumes) was published by the Physical-Chemical Institute of Environmental and Human Protection of the Ministry of Education and Science of Ukraine and the National Academy of Sciences of Ukraine.
