Ivory Lake lies in a 2.2-km2 glacierized cirque basin cut in fissile schist in the western Southern Alps of New Zealand, a region of extremely high rainfall and erosion. Mean annual precipitation at Ivory Basin is 9200 mm, with 75% falling as rain during frequent, mainly high-intensity storms. The proglacial lake, formed by recessation of Ivory Glacier since 1953, traps at least 95% of the basin sediment yield. Bathymetric surveys of the lake were conducted over a 10-yr period (1976-1986) to determine sedimentation rates. Mean annual sediment supply to the lake is 31,000 t, i.e., an average erosion rate of 14,900 t km-2 a-1 from the area of the basin not occupied by the lake. About 60% of the sediment delivered to the lake originates from the steep basin wall, the remainder is probably eroded from the rock beneath the glacier. The sediment yield does not appear to be influenced by the extent of glacial cover. For basins of the Southern Alps cut in schist, annual sediment yield correlates well with annual precipitation or alternatively with annual runoff. Within an international dataset of glacierized and unglacierized basins, precipitation causes greater variation in sediment yield than does degree of glacial cover.