A flamingo stands alone on one bent leg while everyone stares at it, simply because it looks different. The speaker thinks of "The Ugly Duckling" and says they feel that character's pain and despair. That comparison tells us how isolated and judged the speaker feels at the start.
The poem then splits the scene in two. Pink water glimmers and dances around the lilies, but the water around the speaker stays "deadstill," as if happiness is happening everywhere except here. Then the mood turns. Light and warmth come through the dark skies and touch the speaker's body, giving it an "angelic shine." Suddenly the stares become admiration, and the speaker "steals their attention."
The final line, "The water is mine!", is a triumphant claim of space and belonging. The poem moves from loneliness and shame to pride, and the exclamation marks make that ending feel joyful and a little defiant. Being different, it suggests, can become the very thing that makes you shine.