After the formation of the Aidar-Arnasay lakes system in the 70s of the last century, only freshwater plankton species (the Syrdarya river basin) were encountered here, which over the past 20 years, in the process of salinization of the lakes, have been replaced by halo-tolerant fresh and marine species. Since the beginning of 2019, once a season, hydrobiological studies have been carried out on the system of lakes, during which the species diversity of zooplankton was studied. As a result of which 68 species were identified, of which: 38 species - Rotifera, 12 species - Cladocera and 17 species - Copepoda. For the first time in the system of lakes, Copepoda species were found: the marine harpacticide Onychocamptus bengalensis, Swell, and halotolerant freshwater cyclops: Cyclops heberti Einsle, Acantocyclops venustus Norman & Scott, Paracyclops fimbriatus Fisher. It can be noted that the so-called Reman effect is characteristic of the current plankton state of Aidar-Arnasai lakes, according to which a minimum of marine and freshwater animal species is observed in the brackish zone close to fresh water (with salinity of 5–8%).