PB4Y downhill scan in Lake Washington showing a two large boulders west of the plane.

If you take a look at this sidescan image of the PB4Y you will see two large signatures off the nose of the plane. These are the infamous boulders that are occasionally dropped on by mistake. You can see that due to their size and close proximity to the plane that they could easily be mistaken on a depth sounder for the plane which typically has a poor signal due to its positioning.

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With this said, divers who are familiar with this site are able to swim from the rocks down to the plane.