  We present a theoretical study of the hydrodynamic properties of a quantum
gas of exciton-polaritons in a semiconductor microcavity under a resonant laser
excitation. The effect of a spatially extended defect on the superfluid flow is
investigated as a function of the flow speed. The processes that are
responsible for the nucleation of vortices and solitons in the wake of the
defect are characterized, as well as the regimes where the superfluid flow
remains unperturbed. Specific features due to the non-equilibrium nature of the
polariton fluid are put in evidence.
