A species checklist is presented for a stretch of the seasonally flooded Macal River in the Cayo District of Belize, together with preliminary phytosociological data for the primary riverine communities. A total of 229 species were recorded in the seasonally flooded riparian zone, representing 7% of the flora of Belize. Results of quantitative sampling indicate that Inga vera subsp. vera dominates the river corridor. Other important woody associates include Cuphea calophylla, C. utriculosa, Calyptranthes bartlettii, C. lindeniana, Lindenia rivalis, Pleuranthodendron lindenii, Calliandra tergemina and Nectandra salicifolia. One of the most significant threats to riparian vegetation in the region is the Chalillo Dam upstream of the study site. The current work provides baseline floristic and ecological data for this threatened riparian habitat and documents the structure and composition of vegetation that exists downstream from the dam before its construction.