Went to the Sumidero Canyon today.  The canyon is located just outside of Tuxtla off the road between San Cris and Tuxtla.  We drove with fellow travelers which made it easy for us not having to go by bus.  Coming down out of San Cris it felt like we were almost at sea level again.  The canyon walls rise up to 2,625 feet as your lancha (fast boat) speeds through the canyon.  It takes almost two hours.  Today there were so many boats that it made for one choppy ride bouncing us around in the boat like a carnival ride.  Wildlife including herons, vultures and crocodiles could be seen at the shore.  In spite of the beauty here it is one of the most polluted rivers in Mexico.  We could see trash accumulating in one grotto area.  Part of the price of admission goes to pay for cleanup.  We could see some trash boats hauling stuff out of the water.  Apparently solid waste from Tuxtla ends up here too.  Kids were swimming down river near the boat ramp.  Seems like a bad idea.  Hope they can figure out how to keep this area in the pristine condition that it deserves.