What were some of the rumors the reporter heard?

From the text:

It was a random shot, and yet the reporter’s instinct was right. Gatsby’s notoriety, spread about by the hundreds who had accepted his hospitality and so become authorities on his past, had increased all summer until he fell just short of being news. Contemporary legends such as the “underground pipe-line to Canada” attached themselves to him, and there was one persistent story that he didn’t live in a house at all, but in a boat that looked like a house and was moved secretly up and down the Long Island shore. Just why these inventions were a source of satisfaction to James Gatz of North Dakota, isn’t easy to say.