As the border organizer for Sierra Club's Environmental Justice program, I bounce back and forth across the U.S.-Mexico border supporting grassroots environmental activists. More than the food, language, or currency, the biggest difference from one side to the other is what issues are considered "environmental." Perhaps nowhere else on earth is there such a long border between such a rich country and such a struggling one, and this disparity seems to carry over to which issues take priority. Reynosa residents head to a community water source. Photos: Oliver Bernstein. For example, Laguna La Escondida in Reynosa, Mexico, a water source …