What's the meaning of "Wailaree"?

kenosaka jp Japan
The movie, "My week with Marilyn" is out now!

In a song called "The River Of No Return", Marilyn Monroe sang a word "Wailaree". What's the meaning of this word? Is this a coined word from "wail"?

If you listen
You can hear it call
Wailerie (wailerie)
There is a river called
The River of No Return
Sometimes it's peaceful
And sometimes wild and free
Love is a traveller
On the River of No Return
Swept on forever to be lost
In the stormy sea
I can hear the river call
March 2012