Against the backdrop of intensified global warming and the growing importance of carbon cycle research, inland water bodies in karst regions have emerged as efficient carbon sinks, underscoring the necessity for their accurate identification and comprehensive characterization. Guangxi, a representative karst region in China, lacks a systematic classification of its karst and non-karst lakes and reservoirs (collectively referred to as lacustrine systems), posing a critical gap in both regional and national-scale research. This study aims to address this gap by providing foundational data for future studies of karst lacustrine systems and informing evidence-based strategies for aquatic ecological conservation and management. A total of 788 lakes and reservoirs in Guangxi (each with a surface area exceeding 10 ha) were analyzed using multi-source geospatial datasets including Lake-Topo Cat, World Karst Aquifer Map (WOKAM), and the Global Lithological Map (GLiM). Through GIS-based delineation, morphological features (area, storage capacity, shoreline length) and catchment characteristics were extracted. Lacustrine systems were classified into four categories based on the proportion of karst lithologies within their catchment areas: karst (>75%), semi-karst (35–75%), weakly karstic (10–35%), and non-karst (<10%). A random forest model was subsequently applied to quantify the influence of various environmental variables—climatic (annual precipitation), geological (lithology), topographic, and anthropogenic (population density)—on the spatial distribution of karst lakes and reservoirs. The research shows: (1) Karst lakes and reservoirs are abundant, comprising 314 of the total (40%) and predominantly situated in peak cluster depressions and dissolution basins within central, north-western, south-western, and north-eastern Guangxi.; (2) Karst lacustrine systems exhibit the largest individual surface area (98.25 km2), maximum storage capacity (10,260 mcm), and the most complex shoreline morphology (up to 554.97 km), yet their average area (1.07 km2) and median storage (1.30 mcm) suggest a predominance of small to medium-sized water bodies with a few large outliers; (3) Karst catchments are overwhelmingly dominated by carbonate sedimentary rocks (>90%), in contrast to non-karst systems, which are primarily underlain by siliceous clastic lithologies; (4) Variable importance analysis from the random forest model reveals that carbonate rocks (37.0%), siliceous clastic rocks (28.87%), and annual precipitation (28.0%) are the most critical determinants of karst lake and reservoir distribution. This study presents the first comprehensive cartographic inventory and morphometric characterization of karst lakes and reservoirs in Guangxi. The results highlight lithology—particularly carbonate dominance—and climate, especially precipitation, as primary controls on karst lacustrine formation. The findings not only fill a longstanding data gap in regional hydro-karst research but also provide a scientific basis for watershed management and aquatic ecosystem conservation in karst terrains.