How do you say 'the sea' in French?

By the sea is "au bord de la mer", "Ã? la mer" in the sense of "seaside".

Ex: I'd like to have a house by the sea: j'aimerais avoir une maison au bord de la mer.

It is "par la mer" when an action is done bythe sea.

Les rochers sont battus par la mer : the rocks are beaten by the sea.