From wiki on the Rio Grande - "Navigation was active during much of the nineteenth century, with over 200 different steamboats operating between the river's mouth close to Brownsville, and Rio Grande City, Texas."
As far as the Rio Grande not reaching the sea. Is that still the case? It looks like it does from Google Maps. I know at one time there was a sandbar blocking it but I read the spring flow washed it out to sea a few years ago.
It is always fascinating to see the irony in the world. One area can't get a drop of rain and a few hundred miles in another direction there is flooding. Widlfires in one place and snow in another.