With the construction and operation of water infrastructure in river basins, significant alterations have occurred in the original habitats, leading to changes in the patterns of juvenile fish resources and the spatial distribution of fish spawning grounds. As a result, considerable attention has been devoted to studying the patterns of juvenile fish resources and the characteristics of spawning grounds in various sections of the Yangtze River mainstream. The dam downstream area has emerged as a focal point for investigating fish spawning habitats. However, due to constraints such as hydrological conditions and topography, localized studies on the spatiotemporal patterns of fish spawning and early life stages in the dam downstream area have been challenging. Extensive research has been conducted on the dynamics of fish community structure in the middle and lower reaches of the river, as well as the interconnected lakes, encompassing changes in fish populations and the mechanisms driving river-lake migrations. However, limited research is available on the coupling relationship between concentrated spawning habitats, fish resources early in their life cycle, and river environments in the upstream tributaries of lakes. Exploring the patterns of early-stage fish resources and concentrated spawning in the upstream tributaries of large lakes is equally important for the conservation of aquatic fisheries resources. The upstream rivers of lakes serve as crucial ecological zones for migratory fish reproduction in river-lake systems and play a vital role in replenishing juvenile fish resources for such species. The Xitiaoxi River, an important supplementary tributary of the Tai Lake, also serves as a crucial conduit for fish migration in the southern the Tai Lake basin. It is home to a nationally protected gene pool and boasts abundant fish resources. The East Mountain section below the Jiangdong Power Station in the Xitiaoxi River is a concentrated breeding site for regional fish populations. Moreover, the area downstream of the Jiangdong Power Station provides favorable hydrological and topographical conditions, making it an ideal location for conducting localized studies on the spatiotemporal patterns of juvenile fish resources. To investigate the intrinsic relationship between the variables of the downstream river habitat and fish resources under the influence of the power station, this study conducted a 90-day survey of fish resources and spatial-temporal patterns using a shallow type I plankton net in the Dongshanjiang section of the Xitiaoxi river from April to July 2022. The survey obtained 24455 fish eggs and 24325 larval fish, with a daily average density of (0.5±0.7) ind/m³ and (0.5±0.6) ind/m³, respectively. Using morphological and molecular biology methods for identification, a total of 35 fish species were identified, belonging to four orders, 14 families, and 22 genera. Hemiculter bleekeri, Squalidus argentatus, Cyprinus carpio, Carassius auratus, Saurogobio dabryi, and Culter mongolicus had relatively high numbers of eggs and larvae. The fish resources included 9 species of benthic egg-laying fish, 5 species of pelagic egg-laying fish, 9 species of adhesive egg-laying fish, and 12 species of drifting egg-laying fish. Late May, early June, and late June were the peak spawning periods. The sampling results evidenced that benthic and adhesive egg-laying fish, which use aquatic plants as attachment substrates, were dominant on the left and right bank sample lines, whereas drifting, adhesive, and pelagic egg-laying fish dominated the river center sample line. The redundancy analysis results evidenced that water temperature, flow rate, and water level influenced the number of fish eggs and larvae in the area to varying degrees, with water level and flow rate being the main factors affecting fish reproduction, and egg production increasing significantly after rainfall. Based on the results of egg harvest and egg development stage, the sampled river section and the upstream river of Dongshanjiang in the Xitiaoxi River were determined to be a composite fish spawning ground. The fish resources in this spawning ground were abundant, and the habitat was suitable for fish reproduction and nurturing. The discharge of the power station had a certain effect on fish reproduction, and moderate ecological scheduling could meet the needs of fish reproduction, which was of great significance for the protection of fish diversity and fishery resources in the Tai Lake.