Evidence is presented showing that the deep waters in the Saguenay Fjord are flushed at a rate that appears to be significantly higher than other sill fjords with comparable bathymetry. Interval waves in the St. Lawrence estuary, with magnitudes of up to 60 m, provide a mechanism for bringing up dense water, semidiurnally, to the level of the seaward sill. Providing the density of the deep water in the fjord's outer basin is less than that at sill depth, a density flow develops and descends into the basin. Estimates of volume and kinetic energy fluxes of the plume suggest that, by itself, this is insufficient to explain the high flushing rates observed. Other processes, such as internal waves, which must be operative in carrying energy into the deep basin, are discussed.Key words: estuaries, sill fjords, mixing, circulation, coastal