Tennessee's Duck River in National Geographic

The National Geographic magazine that hit newsstands and mailboxes Tuesday features a story about Tennessee's Duck River -- hailing it as one of four of the most biodiverse places in the world.

In the magazine, the Duck joins the company of Table Mountain in South Africa, a cloud forest in Costa Rica and a Pacific Ocean coral reef in French Polynesia.

At those locations, National Geographic photographer David Liittschwager set out to capture as many local species in one cubic foot of space as he could.

What makes the Duck River special enough for such attention?

Time and geography, according to Leslie Colley, director of the Nature Conservancy's Duck River program.

"The glaciers never came this far south, so the creatures have lived there for eons," she said. "And it's largely unimpounded (by dams) so it has natural flows with the shallow shoals and (deeper) runs that mussels and many fish depend on.

"It's