Max, you're absolutely right. Somebody somewhere must know something about the history of this song. My money is on Bruce O. Don't give up, though. I asked the same question about Pop Goes the Weasel and a fantastic thread resulted--one that should be in the thread hall of fame.
By the way, have you ever sung it backwards?

Dream a but is life
Merrily, merrily, merrily, merrily
Stream the down gently
Boat your row, row, row.
You do the melody backwards, too. It's a little difficult to conceptualize. Remind me at the next HearMe and I'll demonstrate. Never sung it that way as a round, though...

Aloha,
Mark