AbstractThe growth and production of the annual floating‐leaved water chestnut (Trapa natans) were studied during summer 1993 at three sites at Lago di Candia (Northern Italy). These sites were subjected to different levels of harvesting from 1986 to 1992. Site USD was the unharvested control site; site 30S was harvested in alternate years (1987, 1989 and 1991); site 30D was harvested every year from 1986 onwards (except 1989) and moreover was sown during 1990, 1991 and 1992 with 8, 4 and 4 seeds/m2, respectively. Despite differences in seed density in the sediment, reflecting different harvesting and sowing practices, neither the biomass of water chestnut nor the fruit production were statistically different in the three sites although the production of buds, flowers and fertilized ovaries was higher at site 30D. In this site, where the plant density was four times lower, water chestnut increased the number of rosettes per plant two to fourfold. This productivity increased the population's invasive capacity. In Lago di Candia, water chestnut grows to 3 m in depth and it competes successfully with hornwort (Ceratophyllum demersum) in the littoral zon