T.S. Eliot's reference to the river as a "Great Brown God," etc. might
be one good place to look. I don't have the book on hand right now, but
I do recall that the essay with this reference is reprinted in the
edition of _Huck Finn_ edited by James Phelan and Gerald Graff with the
subtitle "A Case Study in Critical Controversy" (Bedford, 1995).
Best of luck,