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Ceratium furcoides is a dinoflagellate that exhibits invasive behavior in the aquatic ecosystems of South America and has been expanding its range in recent years. In this study, we monitored 151 municipalities in southern Brazil between 2012 and 2019 with the objective of detecting and recording the species' occurrence and abundance in the state of Rio Grande do Sul, as well as to examine its expansion and persistence pattern. Ceratium furcoides was recorded in 84.1% of the monitored municipalities, in all three of the state's hydrographic regions (HR). Spatially, the Guaiba HR showed the highest density for the species (10,912 cells mL−1); in temporal scales, 2014 and 2015 displayed density peaks, usually in the summer. The cumulative area invaded by C. furcoides gradually increased, reaching 266,625 km2 in 2018, corresponding to about 94% of the state; however, the highest expansion rate (3142 km year−1) and longest distance covered (40.4 km) occurred in 2012, during its introduction. The expansion varied over the studied years, initially heading toward HR Littoral and Guaiba (between 2012 and 2014), followed by a steady period (2015–2017), and subsequently a progression toward HR Uruguay (2018). The frequency analysis showed that persistence was short in most of the municipalities. The results indicate that local environmental characteristics, especially temperature and precipitation, could be key for the invasion and development of the species. Given its rapid expansion, statewide dispersibility, and extremely large bloom formation, Rio Grande do Sul looks to be C. furcoides' second home. [ABSTRACT FROM AUTHOR]