She was a pretty little thing, but I fear the libido of the young men she encountered in here would be at a low ebb.
I do understand what "libido" means, as well as "ebb". The dictionary definition of "ebb" tells me that it usually refers to the flow of the tide and has the connotations of a tide backing away or the flow of anything else for that matter falling/decreasing in intensity. In noun form, it's typically used this way: "on the ebb" which means to "be on the fall".
But the thing is the phrase "at a low ebb" sounds to me rather like "at a low level" or "at a low flow". "Ebb" is not supposed to mean so—where "ebb" already means a dwindling amount of something, how can it be labelled low? And I haven't seen at used before "ebb" anywhere before.
What exactly does "at a low ebb" mean and in which sense is it used?