This photo popped up while I was googling for something else.
<http://otrwjam.files.wordpress.com/2013/03/0187.jpg>
Searching within paddleducks brings up a few references, in the original Yahoo version.

Googling brings up lots:
It is steam propelled: <http://en.wikipedia.org/wiki/American_Queen>
<www.americanqueensteamboatcompany.com>
<www.steamboats.org/steamboat-pictures/american-queen.html>
Lots of photos:
<www.bing.com/images/search?q=paddle+american+queen&qpvt=paddle+american+queen&FORM=IGRE>

Roderick B Smith
Rail News Victoria Editor

I modified the original post with a few links.  It really is steam.

Roderick B Smith
Rail News Victoria Editor

And also has two diesel-powered screws or thursters, which were at one time used most of the time