Lol, no, the meaning doesn't make sense at all - unless it was a very slim lake, hehe. Maybe a lake on a brook which is only just wide enough to be called a lake rather than just part of the brook . . . now I'm just thinking about that *way* too much!
I'm not sure whether I found Linneth or just made it up. I used it in a fantasy story when I was in my teens, and I rediscovered it recently and thought "hey, that's actually not bad". It's basically a variation of Lynette, so it has the same meaning of "little lake".