The speaker has finally reached the sea, something they have wanted for a long time, and the moment feels quiet rather than triumphant. Instead of celebrating, they step back and strip themselves of importance: they have made themselves "commissioner of nothing," a wry, almost joking way of giving up authority and ambition. There is no job to do here, no one to command.
From that emptiness comes a small act of will. The speaker decides not to fear "a bear spirit," which seems to be a presence, perhaps something wild or unsettling, that comes with the water. The title's pun, "Water bearish," hints at this mix of the watery and the bearlike. The last lines are ambiguous. "Poor and mean" could describe the speaker, or the spirit, and "bearing me up" plays on the bear again, suggesting that something humble and rough is holding the speaker steady. The mood is calm, spare, and a little playful, with a sense of acceptance.