Measurements of the rate of dissipation of kinetic energy around a shallow seamount in the eastern North Pacific show that mixing there is 100 to 10,000 times as large as that far away from the seamount. If such values are typical of other seamounts, mixing across density surfaces in the ocean occurs mainly at their boundaries, and topographically induced mixing may help to explain the discrepancy between the observed intensity of mixing in the interior of the oceans and that required to satisfy models of ocean circulation.