The Gasp¿ Current, situated in the western Gulf of St. Lawrence, is an intense, buoyancy-driven jet, which is fed by freshwater runoff from the St. Lawrence River. This coastal current is known to exhibit frequent episodes of instability, culminating in backward breaking waves as well as filaments and eddies. We investigate the observed mesoscale variability in a series of numerical simulations, employing a two-layer frontal geostrophic model that focuses on baroclinic dynamics. Unlike previous studies, we allow for large-amplitude variations of the interface depth, with the possibility of outcroppings, as well as two-way coupling of the dynamic pressures in each layer. It is found that the growth rates and length scales associated with the early evolution of disturbances compare favorably with those observed. Moreover, the mesoscale features resulting from highly nonlinear interactions closely resemble those seen in satellite data. ¿ 1999 American Geophysical Union