The aquatic macrophyte, Hydrilla verticillata is a serious invasive plant in many countries. In East and Central Africa, H. verticillata is present in some water bodies, but not considered a weed. Hydrilla verticillata leaves collected in this region often appear to be chewed, and many stems are missing their apical meristems. Based on this damage, we hypothesized that fish were responsible. To test this hypothesis, fish were collected in Lake Bisina, Uganda, their stomach contents examined, and plant damage putatively caused by fish was quantified. Seventeen species of cichlid fish were collected and H. verticillata leaf tissue was found in the stomachs of four species, demonstrating that fish consumed H. verticillata. A survey of plant damage in the same lake revealed that the majority of branches were missing apical meristems, and about half of nodes had leaf damage. Eight of the fishes we collected are on the list of threatened species maintained by the International Union for the Conservation of Nature, but only one of these was included in the justification for designation of Lake Bisina as a wetland of international importance (RAMSAR site). We recommend that the other seven species be added to the RAMSAR justification.