From notes I've found on Spanish websites, which I hope I'm interpreting properly, this song ("A Rianxeira," or "Ondiñas da nosa ria") was written in 1947 by Xesús Frieiro Dourado for the Coro Catelao de la ciudad de Buenos Aires. It premiered in 1950. There are now multiple versions. Related is the Galician coro "Bernardo del Rio", which uses its tune.