Morning on a river, and somewhere out on the water, someone in a boat says "ouch." That's the whole scene, and it's surprisingly funny and surprisingly true. The poem suggests that the light has hit this person, probably sudden and bright as the sun clears the water or the trees, and the sharp little word is the body's honest reaction. It isn't a grand statement about beauty. It's a wince.
What I like is how the poem treats that small, unguarded sound as a reply. The light arrives, and the word answers it, almost like a conversation. The speaker seems to be listening from a distance, since the word comes "from a boat" without us seeing who says it. That keeps the moment anonymous and a little mysterious.
The mood is quiet, fresh, and gently humorous. Dawn is often described in solemn, glowing terms, but here it can be a bit too much, and the poem lets us smile at that while still feeling how bright and vivid the morning is.