Though a tidy and careful poet, Elizabeth Bishop only occasionally writes formal stuff. She has a sestina and a villanelle in her collected poems, and sometimes she'll choose a rhyme scheme to work with, but this particular poem is completely free verse (written without a consistent rhyme or meter).
The lines are of pretty equal length, and are relatively short. The evenness of the lines gives an impression of control (something Bishop is always trying to achieve) and their short length works to measure out the careful description in the poem. It almost feels like a really long, descriptive list; and it's all one stanza!