We present here a first attempt to validate a regional three-dimensional (3-D) physical–biological coupled model of the Gulf of St. Lawrence with coincident Advanced Very High Resolution Radiometer (AVHRR)-derived sea surface temperature (SST) and Sea-viewing Wide Field-of-view Sensor (SeaWIFS)-derived Chlorophyll-a (Chl-a) data. The analysis focused on comparisons between remotely sensed data and simulated as well as in situ temperature, salinity, Chl-a, and nitrate. Results show that the simulated and AVHRR-derived fields of SST were qualitatively and quantitatively in agreement with in situ measurements. By contrast, marked differences were found between the simulated and SeaWIFS-derived fields of Chl-a, the latter comparing better with the freshwater-associated turbidity simulated by the model. Simulated temperature, salinity, nitrate, and Chl-a data compared well with coincident in situ measurements, and it is then suggested that freshwater-associated turbidity related to the river discharges largely contributed to the Chl-a retrievals by SeaWIFS in the Gulf's waters when using the standard OC4v.4 algorithm and atmospheric correction. Nevertheless, the striking agreement between SeaWIFS-derived ocean colour data and the simulated freshwater-associated turbidity allowed to validate the regional estuarine circulation and associated mesoscale variability. This result brings support to the model's ability to simulate realistic physical and biogeochemical fields in the Gulf of St. Lawrence.