The presented species list of zooplankton is a summary of long-term observations that took place on the small river Stepnoy Zai, situated in the industrial zone of the Middle Volga region of Russia. The sampling took place in May, July, and September yearly from 2008 to 2019 from 4 sampling stations along the river Stepnoy Zai. The sampling stations were situated upstream and downstream of municipal wastewater discharges of the four cities located in the upper (Bugulma, Leninogorsk), middle (Almetievsk), and lower (Zainsk) reaches of the river. Sampling was performed using Apstein Net from the upper water horizons. Samples were concentrated to 100 ml, and fixed with 4% formaldehyde solution.

This work was funded by the grants allocated to the Federal State Budgetary Institution "Administration of Hydrometeorology and Environmental Monitoring" for the monitoring of surface waters of the Republic of Tatarstan (Russia) and by the grant allocated to Kazan Federal University for the state order in the sphere of scientific activities, project № FZSM-2024-0004