Why 'River' has a capital R

Naming words are nouns. Only proper nouns (names of particular people, places or things) start with a capital letter: Delhi, Jahnavi, Gopi. Common nouns don't: girl, village, river.

So why does the writer write 'the River', with a capital R? 'River' is a common noun! Look at what the River does in the story:

The River speaks: "Dear, dear! What's the matter?" It laughs at Jahnavi for being scared. It has a sleepy voice. It's in a hurry: "I've got to hurry to reach the sea, you know." It gives advice. At the end it chuckles and promises to tell her about ships.

Those are things a person does, not water! The writer has given the river human qualities. Once a thing acts like a person, it becomes a character in the story.

And a character has a name. That's why the capital letter: the writer treats 'River' like 'Jahnavi' or 'Gopi', as the name of someone in the story.

See both in one place: "a green lizard slid down to the river's edge" (small r: just water) and "said the River, for it was the River" (capital R: the character who talks).

You can do this too! If you give the wind, the sea or an old tree a voice in your story, a capital letter tells your reader: this one is going to speak.