The speaker starts out in a tiny, safe bubble, happily walking, running and dancing in it. Then the bubble becomes water, and the world gets bigger. Growing up, the speaker says, brought curiosity, and the poem turns into a search: is there a bottom, and what does it look like? The short, repeated lines "I want to know" and "As far as I can go" make that urge feel stubborn, almost obsessive.
The ending is the strangest part. After swimming deeper and deeper, the speaker claims to "know the truth" and feels something they hesitantly call peace, and even happiness. Then comes the last line, "Well aren't I a dumb little fish?" It could be self-mockery, or it could hint that this calm is a warning sign, since the dive has gone so far down. The poem doesn't settle which. The mood is gentle and curious at first, then quiet and a little unsettling, leaving the reader unsure whether the speaker found peace or just gave in.