Dinoflagellates of the Ceratium genus form non-toxic blooms in freshwater ecosystems, generating diverse ecosystem, landscape and water supply effects. In this study, we report for the first time in Chile the presence of the invasive species Ceratium furcoides. Since January 2012 to December 2013 the species abundance and its morphology were studied in the urban lake Lo Méndez. Limnological characteristics of the lake were also described. Results showed high abundances throughout the year (average of 4440 ±3153 ind./l) with seasonal changes and blooms in autumn (maximum 19108 ind./l), which were mainly associated with high concentrations of total nitrogen, nitrate, and ammonium. The morphology of C. furcoides showed changes in the total length and number of horns of the hypotheca, which were related to the environmental conditions and its abundance. These morphological changes could constitute a competitive advantage to colonize, stay and grow in hypertrophic freshwater ecosystems.