Which one is the odd one out and why??

The last one because it is only 1 word or it is the only word that doesn't start with "La ...."?

Provence is the only one that isn't a body of water.

La Manche = the English Channel
La Mediteranian= the Mediterranean Sea
La Provence= a region of France
La mer du nord= the North Sea
L'atlantique= the Atlantic Ocean

La Provence. It's the only one that isn't a waterway.

Great minds and all that. We must have posted simultaneously.

Thanks mac11 & Merry Andrew
I didn't know the answer and now I learned something new. I guess I could have looked up the meaning of the words, but to me guessing is more fun.