Satellite images and hydrographic data show episodic flows of Scotian Shelf Water (SSW) across the Northeast Channel to Georges Bank. These flows carry nutrients, plankton, and larval fish and may play an important role in the ecology of Georges Bank. Despite their importance, there is yet no clear explanation of the crossover mechanism. We show here using numerical model results and hydrographic data that the jet flowing along the front between the relatively dense Slope Water and the light Shelf Water is a primary factor in driving SSW crossovers. The crossover of SSW depends on the density difference between these two water masses.