I was attempting to reply to this thread in the Man From Tallahassee section
http://www.thefuselage.com/Threaded/showthread.php?t=73822
but discovered that I could not since it was more than 320 days old.

Anyways, the gist of the thread was that in ATOTC, we get a clear shot of the Barracks.
http://gallery.lost-media.com/displayimage-1163-89.html

There was no indication of a body of water in the vicinity of the Barracks, which should make it impossible for Locke to take a walk to where the sub was located. The OP (ikonn) argued that this was a pretty big plothole. Eggtown presents further proof that this is true.

http://gallery.lost-media.com/displayimage-1379-143.html

The boathouse is obviously located near the Barracks on body of water. This body of water is not in the shot of ATOTC. I love how we are just supposed to ignore this.

It's not impossible to walk to a lake. Just because you can't see it in the shot from ATOTC doesn't mean it's not anywhere around. It could be just out of the shot. We don't know how long they were walking before they got to the lake. I'm not saying that I'm definitely right about this, but I wouldn't consider it to be absurd.