Key parameters of coastal upwelling dynamics in the St. Lawrence estuary are inferred from moored thermistor observations, using a data assimilative technique based on a dynamical model that has terms representing upwelling, vertical mixing, and residual heating/advection. The inferred time series of upwelling velocity, w(t), agrees generally with a time series calculated from a more conventional regression calculation based on the upwelling term alone. In each case, w(t) is highly coherent with alongshore wind stress, indicating that coastal upwelling dynamics are predominant in this region. We found data assimilation to be superior to the simpler regression technique in two ways. First, the inferred upwelling time series is more accurate, as gauged by coherence with wind stress. Second, data assimilation allows the additional inference of other dynamical parameters, such as the vertical diffusivity. The thermistor array thus indicates that the dynamics of this region are largely related to Ekman upwelling, with vertical mixing also being important.¿ 1997 American Geophysical Union