I don't know if this was the largest. Both the mediterranean and the Black sea, each a lot larger than any water body in America.

Anyway, both of those were dry at one point and the water of the oceans broke through. The Black sea went from low lying valley (akin to the dead sea valley, but much bigger) to open sea in less than a week.

I don't know, but that even seems to me must have been pretty spectacular (to watch from a SAFE distance).