Starting in the sunny shallows, the poem takes the reader on a slow dive down through the ocean, and the mood darkens with every stanza. At the surface, children play among shells and colorful fish, and the speaker sounds cheerful, almost content. Deeper down, the sea grows bigger and stranger, with whales, shipwrecks and swarms of life. Then comes the abyss, where light disappears and toothy monsters lurk. At the very bottom, the speaker feels tiny and uneasy, noting that no person can reach it and that the pressure would kill.
What makes the poem work is its shift from comfort to awe and fear. The speaker seems fascinated by the unknown, asking what wonders might be hiding in the dark. The final stanza turns to the reader with a warning: the pretty blue ocean is only one side of it. The simple rhymes keep the tone almost like a children's rhyme, which makes the darker images feel quietly unsettling.