"They are at the lake" or "They are at a lake"?

[Nevermind]

Hi,

I'm wondering if I have to use "at the lake" if I don't mean particular lake. For examle, I see a picture of boys who are at a/the lake?

Cheers.

[Beeesneees]

You need an article.
If it is a particular lake, then use 'at the lake'.
Otherwise use 'at a lake'.
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Cheers m' dears!