A hundred miles long, looking on the map like a great fish butting its head against Manhattan, Long Island was for many years celebrated as the longest island in the (continental) United States. Too bad for the folks on the Island who staked their entire identity on that distinction. It turns out that Long Island is not technically an island at all! It's separated from the mainland by a river the East River. No shit!
Now the longest island in the continental U.S. is Whidbey Island in Puget Sound which looks on the map like a strand of seaweed pointing nowhere in particular.