From this story on ksat.com:
_An investigation has been launched by the Zapata County Sheriff's Office after an American claimed he and his grandson came under fire on Falcon Lake while they were fishing. The fisherman told authorities a group of men in green fatigues opened fire on them earlier this month. Sheriff's officials said no one was injured, but they believe the shooting was not cartel related and shots may have been fired by members of the Mexican military. Falcon Lake is a 60-mile-long reservoir on the Rio Grande, shared by the U.S. and Mexico. Officials added this latest incident happened on the Mexican side of the lake after the fisherman apparently crossed the international boundary.