It's both - evaluative and imaginative interpretations are the key to an A* response. Smith sees the river as a possessive, wily and borderline pyschotic old man whose capriciousness comes with the powers bestowed on him by nature. Hence he is "god-like".The whole poem is possibly an extended metaphor where she imagines the personality of the river as being closer to a slightly lecherous old man than anything else. This links in with the Greek/ Roman idea that many parts of the natural world were inhabited by spirits or gods. Alternatively, the poem also serves as an extended metaphor to highlight the feelings of an old man at the end of his life. It is possible that the river represents human life and that the old man is at the end of his. However, he still feels, despite his appearance, that he is dangerous hence the mentioning of drownings which may be symbolic or literal.