The distribution and density of hydrilla (Hydrilla verticillata (L.f.) Royle) turions and tubers in two New Zealand lakes were assessed by sampling cores of sediment from Lakes Tutira and Waikapiro each year from 1994 to 1997. Turion and tuber density differed with water depth, with maximum numbers of tubers and turions found in the 1-2 m and 1.5-4 m water depth ranges respectively. A high turion to tuber ratio was observed, with turions accounting for over 80% of the propagules. The relatively low numbers of turions and tubers compared with other reports, and the distribution of most tubers within the shallow water is likely to be associated with black swan grazing (Cygnus atratus Latham), which maintains a canopy of hydrilla consistently 1 m below the water surface.