LAUSR

ABSTRACT Shallow freshwater lakes are vital for ecological and climate regulation, but many are degrading. Although restoration efforts are underway to improve water quality, research on their trophic structures is still limited. Baiyangdian Lake (BYD), a typical shallow lake in northern China, has seen improvements in water quality, biodiversity, and aquatic plant biomass after restoration. However, it remains unclear whether its food web's trophic structure has fully recovered. This study collected various field samples from BYD in 2023 and reconstructed BYD's current trophic structure using δ15N and δ13C stable isotopic analysis. Results indicate that plankton constituted the predominant food source for fish and invertebrates, contributing over 70%. Aquatic plants and macroalgae contributed more significantly to humus and soil organic matter in the sediment than to the main food web. Despite the high biomass of aquatic plants, trophic relationships among fauna in BYD are predominantly reliant on pelagic‐based energy flow pathways. This suggests a potential hysteresis response of its food web structure and ecosystem function to environmental restoration efforts. This study highlights the underestimated long‐term ecological impacts of human activities and emphasizes the need for extended restoration to re‐establish trophic relationships and restore ecosystem health.