Diseased water hyacinth leaves were collected from 5 different ecosystems in Ho Chi Minh City, then followed by fungal single spore isolation. The fungal isolates were morphologically characterized based on their mycelium, fruiting structures, and spores. The frequency of occurrence of each fungal genus was recorded. The pathogenicity of each isolate on water hyacinth was performed at laboratory conditions and the disease severity (DS) was assessed. A most harmful isolate of each fungal genus was tested for its pathogenicity on plants, associated with water hyacinth. The results showed that 106 fungal isolates were discovered, belonging to seven fungal genera, in which Curvularia spp. and Colletotrichum spp. were classified as very frequent groups with 36.80% and 29.24% of occurrence, respectively, while a frequent group of Rhizoctonia spp. (18.87%) and infrequent groups of Trichoderma spp. (5.67%), Helminthosporium spp. (4.72%), Fusarium spp. (2.83%) and Alternaria spp. (1.89%) were observed. The highest disease severity was found in the genus of Colletotrichum spp. (DS 17.2%), followed by Curvularia spp. (DS 12.7%) and Rhizoctonia spp. (DS 7.1%). All tested fungal isolates were infected plants with various levels of incidence from 0% to 100% depending on fungal genera and host plants.