The Internets say "anthem" means an uplifting song identified with a person, group or cause. "O River" is indeed about a particular person: my friend and Thomas S. Wootton classmate Neil Bernstein, lost in the Potomac River February 2023.

With great loss, one understandably seeks answers, and while one can (as the song does) ask The River what happened to Neil, so far its replies have been wordless. Which is to say these asks, like all prayers, are not necessarily unanswered.