In the short story, "The Bass, the River, and Sheila Mant," the young narrator clearly values the river. It is where he participates in his favorite hobby of fishing and sees the girl that captures his attention. The narrator shares that even the stars "seemed to have chosen the river as a guide."

It is the river that allows the young boy to demonstrate his strengths to Sheila. He hopes to gain her attention by showing off his swimming skills and that he can effectively maneuver a canoe. He reflects that he could have "threaded the eye of a needle with the canoe." His hopes to share another of his strengths with Sheila are shattered when she makes the announcement that she thinks "fishing's dumb." Years later, the narrator still ponders Sheila's possible reasons for a dislike of fishing; it seems strange to him that someone could dislike something that he sees as valuable.

Though he chooses Sheila over the bass, the narrator is haunted by this decision. His obsession with Sheila eventually comes to an end, but his love of the river--and fishing--persists.

You're certainly on track with what you've pointed out from the story.  A couple of elements to consider are that the narrator is more comfortable on the river than he is on land.  Notice that when he tries to play softball, he's awkward.  When he's with Sheila at the dance, he's awkward, and she leaves him for an older boy.  But, on the river, he prepares his boat as best as possible to take Sheila to the dance, and he is confident in his angler skills.

Another important point about the river is that, as you pointed out, the boy must choose between the two parts of his life that he holds dear, both of which are connected with the river.  The narrator associates Sheila with the river because she's always sunbathing near it when he's fishing, and of course, the river is the home of his hobby.  So, it is ironic and fitting that the narrator has to choose between his two "loves" when he takes Sheila out on a date and that he has to make his choice while on the river.