A hot tub boat!

The lower picture is from a boat in Lake Union (Seattle). Note the small boat just to right of the edge of the boom.

The upper picture is magnified (poor quality picture due to the distance and cloudy Seattle weather).

It is basically a floating hot tub! Not sure what the fuel is but you can see the chimney and it was emitting very light dark smoke. People were just floating away in their hot tubs surrounded by the 64 degree cold water of Lake Union!