Data from three sequential stations of thermistor chains and current meters along the main axis of the lower St. Lawrence estuary during the summer-fall period in 1978 were analyzed to help understand generation and variability of the internal tide. The Lagrangian (or direct tracing) method has been developed to compute the displacements of internal tides, which can overcome limitations of the Eulerian method caused by the very small vertical temperature gradients. Internal tides of semidiurnal frequency were observed, but diurnal tides were not, in both the time domain and frequency band. The surface diurnal tide behaves like a standing wave rather than a progressive one. Due to the nonlinear interaction of the internal tide, generated locally near the sill, with topography, quarter-diurnal and higher frequency oscillations were also generated. The displacement of internal tides can reach 80, 40 and 30 m during spring tides, respectively, at station 1, and at two downstream stations 3 and 5. The internal tides propagate seaward with attenuation downstream, which mainly results from changing vertical stratification conditions, but may also be partly attributed to wave breaking and turbulent mixing in the upper layer and bottom and lateral friction. The amplitude ratio of S2/M2 is smaller (0.2) for the baroclinic current than for the barotropic current (0.24) at station 1 but becomes larger at stations 3 and 5. This implies the presence of the narrower response frequency band of the baroclinic tide to the barotropic forcing near the generation site. The progressive semidiurnal and quarter-diurnal internal tides were of the Poincare type, which implies a three-dimensional structure. The ''nutrient pumping'' due to the internal tides was confirmed to occur only near the generation region of the internal tide. This convergence zone of higher primary productivity is considered to be equivalent to the ''rotor clouds'' in atmospheric mountain waves. ¿American Geophysical Union 1991