Heather W. answered 06/21/19
Literature instructor, specializing in Shakespeare
Yes -- the mirror and the lake are serving as powerful metaphors in Plath's poem. In the beginning, the narrator is a mirror. A mirror shows what things are ("swallowing" or taking in what it sees with no judgment, as the poem goes). The mirror hangs in the home being constant. However, in the latter part of the poem, there's a shift from the mirror to the lake. A lake does show a reflection, but there's also depth there and movement. The poem references drowning -- consuming and taking in. The woman's youth was lost in that lake and now it's an older woman that stares in. So, there is a slight shift in metaphor, but both the mirror and lake are both doing the same thing: being a consistent truth-teller (as opposed to the moon and candles which the narrator casts as liars).