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Agua Blanca is often described as Cali's biggest slum. It is home to some 600,000 people, many of whom have been displaced from their rural homes by the violence between Marxist rebels and right wing paramilitary forces and other factors such as natural disasters. Left without alternatives they created their own neighborhoods by building makeshift shacks illegally without land titles. There was an awful period a few years ago where the government battled to forcibly dislodge the residents. Finally, the government began to provide basic services to these people and built schools and hospitals. More than 60% of the population of Agua Blanca live in poverty and earn less than US$ 2 per day. Here are a couple links:
http://www.accessallareas.org/aguablanca/background.html
http://www.colombiasolidarity.org.uk/content/view/36/54/
Above photo taken by student Yicel Valencia.