Read this stanza again:

oh! the old swimmin'-hole! in the happy days of yore,
when i ust to lean above it on the old sickamore,
oh! it showed me a face in its warm sunny tide
that gazed back at me so gay and glorified,
it made me love myself, as i leaped to caress
my shadder smilin' up at me with sich tenderness.
but them days is past and gone, and old time's tuck his toll
from the old man come back to the old swimmin'-hole.

the second stanza of the poem

describes the swimming hole
describes how the boy has changed
describes the speaker as a boy
describes how the swimming hole has changed