Should I say "I am by the lake" or "I am at the lake"? Currently I am camping and I do not know how to tell my friend where I am. Thank you for help!
It depends. Is your location the same as the lake's, or are you merely near it?
I am at the lake.
This means that someone going to the lake will find you, because that's specifically where you are.
I am by the lake.
This means you are close to the lake, but not exactly at it. This isn't specific enough to tell your friend precisely where you are, though it does convey the general area.
Either one will work.
I would interpret "at the lake" to mean "in the general vicinity of the lake," while "by the lake" means "so close to the lake I could throw a stone in the lake from here."
"We are at the lake" can also mean "we are at the cabins near the lake" or "we are at the campground near the lake," depending on the format.
Which preposition gets used might also depend on the amount of precision you are trying to provide. If you're setting your email account's autoreply to say:
Sorry, I won't be available until next Tuesday. I'm up at the lake.
then it seems like "at" is a better option. Moreover, if you're trying to give someone directions on where to join you for the campfire tonight, then "at the lake" might be better if you're at a certain location near the lake, such as a public campground. However, "by the lake" might be good if you're on a beach at the lake, as in, "We're by the lake, up near the north boat ramp."