25. Cristina Mittermeier
Mittermeier is the founder of the International League of Conservation Photographers (ILCP) and has been described as "one of the leading advocates who are shining light on the plight of indigenous people, endangered species, and diminishing resources through stunning and inspirational photography." This Mexican-born artist-activist has been working for over a decade to document and bring awareness to the hidden and dwindling treasures around the world. For a sample of her work, read her 2011 piece Farewell to a wild river on National Geographic's website.
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Above: Farewell to a wild river, 2011