I thought of this too, but am assuming it is because the border 'gate' is not directly on the line. Also, someone walking across the bridge is less suspicious than if they had been swimming across with moss over their head for camo. I think they have to make that decision as it happens - it sure would be easier if there was a just a 30 foot electric fence (think big time bug zapper) on the border.

Anyway, the border patrol is what it is, we can't change them in this forum but we can get the cache.