The Mississippi river delta of the US state of Louisiana is a landscape still reeling from Hurricane Katrina, and facing the threat of worse storms to come.
 
The fragile wetlands of the Mississippi delta once provided sufficient shelter from the storms of the Gulf for humans and wildlife.
 
But when Katrina devastated the city of New Orleans four years ago, it changed the natural and cultural landscape of the region. And since then, people have been leaving.
 
Al Jazeera's Nick Clark reports from New Orleans - for the latest in our special series on Rivers Under Threat.