The speaker is a river, given a human voice and human longings. It leaves the warm, sunny valleys where it began, convinced that the gray open ocean will bring it peace. But when it finally reaches the sea, the ocean is wild and black, not peaceful at all. Immediately the river wants to go back and begs the valleys to take it in again. It is too late: the tide pushes inland, the salt water mixes with the fresh water, and the river is changed forever. What was once fresh as rainfall becomes bitter as the sea.
The mood is melancholy and quietly regretful. The poem feels like a fable about leaving safety in search of something larger, being disappointed by what you find, and realizing you cannot return to the person you were before.