Learn French: Nous mangeons au bord du lac.

No, because chez is only used with people, professions, or businesses (meaning "at the home or workplace of"). Since a lake (un lac) is a geographic place, you have to use location prepositions like au bord de (by the side of) or à.

What does au bord de literally mean?

It literally means "at the edge of" or "at the border of". It is the most natural way in French to say you are "by" or "beside" a body of water, like a lake, river, or the sea.

Where does the du come from before lac?

Du is a mandatory contraction of de + le. The expression is au bord de (at the edge of), and "the lake" is le lac. Whenever the preposition de and the masculine article le meet, they must combine into du.

Why does the sentence use au instead of à?

Just like du, au is a mandatory contraction. It is a combination of à (at) + le (the). Because bord (edge) is a masculine noun, "at the edge" would be à le bord, which must always shrink into au bord.

Why is there an extra "e" in mangeons?