I heard this mistake on last night’s Bones. It’s not the first time I’ve noticed it on TV. I suppose one could explain it away by saying that the characters aren’t from the area and don’t know (although they appear to work in the vicinity of D.C.), but who are we kidding here?
Anyway, as a good local boy I feel compelled to state for the record that the estuary running through Maryland and Virginia can be called “the Bay”, “the Chesapeake”, or “the Chesapeake Bay” but not “Chesapeake Bay”. It always takes an article, like rivers do.