At the impact of a plunging liquid jet with a receiving pool, air bubbles may be entrained if the impact velocity exceeds a critical velocity. New experiments were performed in a two-dimensional plunging jet. The flow conditions near the inception of air t the impact of a plunging liquid jet with a receiving pool, air bubbles may be entrained if the impact velocity exceeds a critical velocity. New experiments were performed entrainment were investigated. Two mechanisms of air entrainment were visualized at low jet velocities: by elongated air cavity and by foam bubbles. The breakage of entrained air bubbles was studied also. The results highlight that the bubble breakage process depends critically upon the initial bubble size.