Nitrogen fixation is critical for primary productivity and carbon-nitrogen biogeochemical cycles in marine, riverine, and lacustrine ecosystems. However, research on aquatic nitrogen fixation remains predominantly focused on marine environments. To elucidate research hotspots and trends in freshwater lake nitrogen-fixing microorganisms, this study analyzed literature from the Web of Science database using Citespace and VOSviewer to construct a knowledge map of publication trends and thematic evolution. Results indicate a continuous increase in global publications and citations from 1992 to 2024, with collaborative networks revealing interdisciplinary and multinational research engagement. Cluster analysis identified three core research foci: (1) phosphorus limitation-driven nutrient control strategies and their impacts on cyanobacterial community succession (Cluster 0), (2) functional characterization of nitrogen-fixing microorganisms based onSnifHSgene diversity (Cluster 1), and (3) long-term phytoplankton community dynamics under environmental drivers (Cluster 2). Meta-analysis further revealed: (1) Geographical imbalance in nitrogen fixation quantification, with North America establishing comprehensive indicator systems across diverse water bodies, while Asia and South America prioritize cyanobacterial biomass descriptions, and Europe focuses on regional nitrogen-phosphorus dynamics; (2) Dominance of Cyanobacteria (e.g.,SDolichospermum,SAphanizomenon) in taxonomic studies, with limited research on Proteobacteria and Archaea; (3) Positive correlation between total phosphorus (TP) and nitrogen fixation rates, with a nonlinear threshold (24.97 μg-P/L) regulating fixation in eutrophic systems, while total dissolved nitrogen (TDN), nitrate (NO??-N), and ammonium (NH??-N) exhibit significant negative correlations. Future research should prioritize diversification of measurement indicators (e.g., fixation rates, enzyme activity) to capture niche-specific processes, standardization of methodologies (e.g., acetylene reduction assay, isotopic tracer techniques) and unit systems (area/volume-based metrics), and integration of multi-indicator approaches to enhance accuracy in assessing nitrogen fixation roles. This study synthesizes three decades of research trends, providing insights into frontier topics and guiding future research directions.Keywords: freshwater lakes; nitrogen-fixing microorganisms; Citespace; keyword clustering; research hotspots; nitrogen and phosphorus