The isolated lakes mentioned in this question that are not connected to other water systems exist in nature, namely Lake Maar, which is located in a special type of extinct volcanic crater. 1) Lake Maar is a closed lake with no rivers flowing in or out. The water level balance is mainly controlled by precipitation and evaporation factors. Relatively speaking, the hydrology and sedimentary system of Lake Maar are relatively simple, and it is easy to interpret paleo-climate and paleo-environmental changes; 2) The steam jet eruption is generally located hundreds of meters underground, and the formed Maar Lake has a large depth and thick sediments, which can provide continuous and stable deposition records for tens of thousands or even millions of years; 3) The “deep water, anaerobic” of Maar Lake “The environment makes sediments less disturbed by waves and benthic organisms, which is conducive to the formation and preservation of annual laminae. The existence of annual laminae can increase the resolution of paleoclimate and paleoenvironmental changes to seasonal-annual Scale; 4) In terms of alternative indicators of paleoclimate change, there is a wealth of diversity, such as diatoms, golden algae, algae, chironomid, ostracods reflecting aquatic habitats, pollen and phytoliths indicating terrestrial vegetation, and Various physical and chemical indicators enable us to understand paleo-climate and paleo-environmental changes from different perspectives, and test the reliability of reconstructed data. Therefore, Maar Lake is an ideal place for the formation and preservation of high-resolution sedimentary records, providing rare materials for the development of multidisciplinary paleoclimate and paleoenvironmental changes. Chu Guoqiang, Liu Jiaqi. 2018. Maar Lake in China and its research significance. Acta Petrologica Sinica, A Maar Lake in Longgang. There are various algae and aquatic arthropods in Maar Lake, but whether it can support fish is not certain, there are indeed some There are no fish in Maar Lake. There is also a man-made environment similar to Lake Maar-the upper reservoir of the pumped storage power station, which is a lake that needs to be built on a mountain. Generally, there is no connection with the natural water system. The only exchange is with the lower reservoir-by pumping water from the lower reservoir to the upper reservoir to store energy, and drain from the upper reservoir to the lower reservoir to generate electricity. I have heard from hydropower experts that there will be filtration when pumping water, and theoretically no fish will be sent from the lower storage. But in fact, fish can appear in the library.