Hi,
I moved to MA about a year ago, and I've been wondering the same thing.
I live in Ayer (up in the Northlands as I call it), and there doesn't seem to be a ready supply of large lakes around here. I've been over to Lowell on the river, but I get the feeling that the traffic and police presence on the weekend would be inhibitive.
I do know of a nice lake in Webster if you don't mind the drive.
By the way, I have a flatbottom prop boat, which appears to make us mortal enemies by the gist of what I've picked up on the board. Don't worry though, I like just about anything that floats, with the exception of sailboats.
Where are you?
Jim