(CBS/AP) No one had to twist Robert Redford's arm to get him to narrate an IMAX film about a Grand Canyon river trip.
Redford, a lifelong environmentalist, previously navigated the Colorado River and has a boat on Lake Powell, a manmade reservoir on the Arizona-Utah border created by a dam. He worries about water conservation as a drought threatens the region - and, visibly, the Colorado.
"(The river is) endangered now on a number of fronts," Redford said by phone Monday from his office in Park City, Utah, where he holds his Sundance Film Festival every year.
"Its volume is shrinking because of a megadrought cycle that's now facing the Southwest, and some scientists predict that it could last into the next century," said Redford, who referred to a recent study forecasting that lakes Powell and Mead - another vital storage reservoir on the Colorado - could dry up in the next 13 years amid climate change and increasing demand for water.
The issues affecting the river, a source of water for some 27 million people in seven states, are addressed in a viewer-friendly way in "Grand Canyon Adventure: River at Risk 3D," which opens nationwide Friday.
The film, directed by Greg MacGillivray, features music by the Dave Matthews Band.