The discharge of the St. Lawrence River drives a buoyant jet which extends along the south shore of the lower St. Lawrence estuary and, combining with the northwest Gulf of St. Lawrence cyclonic gyre, becomes the Gasp¿ Current. In both the estuarine jet and the Gasp¿ Current, strong lateral and vertical shears are present. Satellite thermal imagery has shown that the Gasp¿ Current is unstable. Its instabilities are manifested as prominent wave disturbances and eddy features. We use satellite thermal images from 3 different years to show that unstable disturbances are also characteristic of the estuarine jet. We update previous work to show that Gasp¿ Current is both baroclinically and barotropically unstable. Our model studies also show that this conclusion is valid for the estuarine jet as well. Finally, we discuss a sequence of satellite images showing the development of an unstable disturbance apparently triggered by an eastward wind pulse. ¿ American Geophysical Union 1988