Drinking water supplies around the world often contain trace amounts of pharmaceuticals and synthetic compounds that may be harmful to human health. One solution being tried in the U.S. and Europe is to construct man-made wetlands that naturally degrade these contaminants.

The inland Niger delta of Mali is a unique wetland ecosystem that supports a million farmers, fishermen, and herders and a rich diversity of wildlife. But now, the country’s president and Libyan leader Moammar Gaddafi have begun a major agricultural project that will divert much of the river’s water and put the delta’s future at risk.

A dispute between Egypt and upstream African nations has brought to the fore a long-standing controversy over who has rights to the waters of the Nile. The outcome could have profound consequences for the ecological health of the river and for one of the world’s largest tropical wetlands.