A river, a girl and a reflection: Poe builds this short poem from just those three things, then does something unexpected with them. It begins as a compliment to a young woman, "old Alberto's daughter," a name that is all the poem tells us about her. It ends as a portrait of the man who watches her. The river is the hinge. First it stands for her, then, in a quick turn, it stands for him.
The first stanza addresses the water directly ("Fair river!") and calls it "an emblem of the glow / Of beauty." The adjectives pile up: "bright," "clear," "crystal." Transparency is the point, because what the river shows of her is "the unhidden heart." Then comes a paradox: "the playful maziness of art." A maze is meant to confuse, but this one is playful. The girl is imagined as open and intricate at once, with nothing concealed and yet always some new bend to follow. "Wandering water" supports the picture, since the river's winding course becomes the winding charm of her manner.
The second stanza opens with "But," and the poem changes direction. She looks into the water, which "glistens then, and trembles." The speaker then slips in his real subject with a sly "Why, then, the prettiest of brooks / Her worshipper resembles." The river has been demoted to "the prettiest of brooks," pretty but small beside the woman it mirrors. The comparison that follows is neat. Her face lies in the river, and her image lies "deeply" in his heart. Both the water and the heart hold the same picture, and both are disturbed by it.
The verb "trembles" carries that link. It appears first for the water, then again for the lover's heart, "which trembles at the beam / Of her soul-searching eyes." The rhyme of "trembles" with "resembles" makes the same claim in sound, so that the likeness the speaker announces is also heard. Light runs through the poem in the same way. "Glow," "bright," "glistens" and "beam" all suggest sunlight on water, and the last of these turns her gaze into light falling on a surface. "Soul-searching" is a compressed phrase. She looks into the river, and her eyes in turn look into whoever meets them. The poem's last image reverses its first, so that the watcher becomes the thing watched.
The sound design helps. The first stanza has six lines rhymed ABACCB, with the paired "heart" and "art" at its centre. The second has eight, rhymed more steadily as ABABCDCD. Most lines are four-beat and iambic, but they alternate with shorter ones that end on a soft, unstressed syllable ("water," "daughter," "trembles," "resembles"). These feminine endings give a rippling effect, as if each short line were a small wave breaking after a longer one. The dashes that interrupt lines ("heart--", "looks--", "lies--") work like pauses in the current, and they let the speaker hold his breath before each new comparison. The last rhyme, "lies" with "eyes," ties the reflection that rests in his heart to the gaze that put it there.
It is a slight poem, and it doesn't pretend otherwise. Its charm lies in how much it makes of one conceit. Poe is best known for dark, haunted writing such as "The Raven," so this gentle, courtly piece, with its teasing tone and bright imagery, shows a lighter register. The central idea is that we can be known by what we reflect. The river is beautiful because it holds her image, and the lover is moved because he holds it too. In just fourteen lines of comparison, the speaker admits to being as clear, as shaken and as completely filled with her as the water he addresses.