I thought this was going to be about "Moose Boulder," whose existence was (rather unconvincingly, I think) "disproven" a couple years ago, and which begs the interesting question about how we define "Largest Lake."
I thought the same; the alleged Moose Boulder is in my general back yard area and I've thought about doing some "citizen science" on my next trip to Isle Royale.
https://www.atlasobscura.com/articles/moose-boulder-debunked