March 3, 2006—Teeming with jaguars, macaws, and reptiles and peopled by isolated Indians, Brazil's new Tumucumaque Mountains National Park is under threat from loggers and illegal gold miners. Protected in name only, the park has a handful of employees, and even its borders are largely undecided.

Watch as an intrepid team explores the park by boat, skirting raging currents and making contact with tribes. It's all part of an effort to find out who lives here, the status of the local rain forest, and whether the park is safe for travelers.

Next video: explorers bust an illegal gold mine in the park.