over the past months crews of mexican outlaws dressed in black -- brandishing automatic weapons have been robbing them on their boats at gunpoint. >> when the bad guys boarded they were looking for drugs and guns and money. >> sean: falcon lake straddles the international border which falls in the mid of this reservoir. markers in the water separate the united states and mexico. >> international boundaries marked, extended from the dam all the way to just above where we are standing now. this is marker 11. this is -- they are not always in a line they kind of zigzag following the original riverbed. some are closer to the shoreline some are closer to the mexican shoreline. >> right now over my left shoulder or to my left is the river which comes from mexico.