The poem is a quiet act of looking. The speaker studies a patch of water and lists what turns up there: ripples that show the wind, marsh grasses mirrored upside-down, oily rainbow slicks near black mud, a stick, and a white plastic bag with red "Thank You" printed on it. The word "also" keeps the list going, so it feels like the speaker's eyes drifting from one detail to the next.
In the second part, attention shifts to the reflected sky. It rests on the water "without weight or repercussion," and the speaker boils the scene down to stripes: sky, land, land, sky. The reflection makes the sky seem to lie below the land. The plastic bag's "Thank you" returns at the end, now standing alone. It could be gentle gratitude, or it could be a dry, ironic note about litter in a beautiful place. The speaker doesn't say, which leaves the mood calm, observant, and a little uneasy.