Abstract: Background The water quality of drinking water source reservoirs is crucial for residential water supply safety. Zooplankton, as a key component of aquatic food webs, can sensitively indicate ecological changes through shifts in community structure. Human activities such as agricultural cultivation and aquaculture, as well as invasive fish species, may significantly impact zooplankton communities, thereby threatening reservoir ecological functions. Objective This study aims to reveal the spatiotemporal distribution patterns of the zooplankton community in Shanzi Reservoir, a drinking water source in Fuzhou City, during spring, and to investigate its interactions with phytoplankton and fish communities. Methods Water samples were collected from Shanzai Reservoir during spring in 2023–2024. Zooplankton and phytoplankton species were identified, and their densities were analyzed. Concurrently, water quality parameters and environmental factors were measured. Results In spring 2023, 28 zooplankton species were identified, with an average density of (2,932 ±423) ind./L, where rotifers dominated absolutely, accounting for 91.6% of the total density. By spring 2024, species richness increased to 33, while density decreased to (1,490 ±220) ind./L, with rotifers still predominant (86.9%). Zooplankton density exhibited a spatial trend of "inlet > reservoir center" in both years (P < 0.05). Zooplankton density showed significant positive correlations with dissolved oxygen (P < 0.01) and chlorophyll-a concentrations (P < 0.05), and a negative correlation with water transparency (P < 0.05). Fish monitoring in 2023 revealed that the invasive species Tilapia comprised 85.3% of the fish population, whose grazing pressure may have driven zooplankton miniaturization and enhanced rotifer dominance. By 2024, zooplankton diversity indices improved significantly: the Shannon-Wiener index increased from 1.80 to 2.19, and the Pielou evenness index rose from 0.63 to 0.79, indicating enhanced species distribution equilibrium and optimized community structure. Conclusion The spatiotemporal distribution of zooplankton in Shanzi Reservoir is jointly driven by external nutrient inputs and Tilapia invasion. The expansion of invasive fish populations may exacerbate sub-health risks in the reservoir. This study provides insights for ecological management and eutrophication control in reservoirs.