Bonjour Karen,

To supplement Chris' great answer, here is a third example:

le bord de la mer Méditerranée / Baltique = the shore of the Mediterranean / Baltic sea

-> the definite article 'la' is included as it specifies which sea one is talking about

Also, see link here on a similar topic: the-definite-article-or-not

I hope this is helpful.

Bonne journée !