The Tajumulco and Tacana volcanoes soar high above the coffee plantations that cover the hillsides on the border of Guatemala and Mexico. At 4,400 metres, Tacana is the highest volcano in Central America. These two volcanoes are at the heart of a watershed system that is almost a million years old. This system is now under threat by the increasing levels of water pollution from the coffee industry, as well as erosion, deforestation and pollution caused by hillside communities. But it is coffee farmers themselves who are now leading the way in trying to turn around the fortunes of this threatened eco-system. At the river source at the very top of the mountain the water is pure. As it descends it becomes more and more polluted. It's here at the top that the problems begin.