Egeria densa (egeria or dense waterweed) is a submerged, freshwater perennial herb native to South America. It is popular as an aquarium plant and has been transported globally for this use, where it has become an invasive weed in many countries, including Australia. The prolific growth of E. densa makes it highly invasive. It forms dense stands with a canopy at the water surface in wetlands, streams, rivers, lakes and irrigation channels that have with permanent water. These stands scavenge nutrients directly from the water, heavily shade the water and promote thermal and geochemical stratification, while suppressing the growth of phytoplankton and displacing native submersed aquatic vegetation (SAV). E. densa has been classified as an ecosystem due to these impacts. In addition, in amenity lakes it impedes recreational activities and aesthetic values, while it blocks irrigation infrastructure and hydro-electric power plant intakes. I will describe three field research projects that 1) characterise its rapid displacement of native SAV (a mixed charophyte and Potamogeton spp. community) in a constructed wetland, 2) use water level manipulations to maintain a diverse SAV community (Vallisneria australis, P. ochreatus, P. sulcatus) in the presence of E. densa in Lake Mulwala, and 3) tested the effectiveness of a range of management approaches (herbicides and water level manipulations) to control it in irrigation channels. The current known distribution of E. densa in Australia will be summarised, with gaps in knowledge highlighted. Characteristics that make a waterbody susceptible to invasion and management options applicable in natural waterbodies will be discussed.