This is an illustration of a plane wreck underwater. Now, this is obviously is not the wreck of Brian's plane, but it does show a significance, as the plane is crashed underwater. This is significant since Brian crashed in the wilderness, obviously, and the only place for him to land for miles around him was an L shaped lake in the middle of the wilderness. If Brian found a clearing, then the plane would be above ground, maybe even intact, and he could have lived in the hull of the plane, making life much easier for him. Also, since Brian landed in the bottom of a lake, he is unable to access anything in the plane, including the survival kit that he had in the rear.