EL PASO — One of North America’s great rivers is dying.

Stretching nearly 1,900 miles from the Colorado Rockies to the salty Gulf of Mexico, the Rio Grande has been the stuff of Southwestern lore, sustained entire cultures and nourished wildlife in an otherwise unforgiving part of the planet.

The Rio Grande is the third-longest river in the United States , exceeded only by the Yukon and the combined Mississippi and Missouri Rivers. Yet this summer it nearly stopped flowing from Colorado into New Mexico. The muddy water that does flow into Texas is something of a mirage, released from reservoirs or even imported from faraway basins. Drained by farmers, divided by treaty, feuded over in courtrooms and neglected when not pumped and drained, the Rio Grande is at once one of America’s most famous rivers and one of its most abused.

The problem is compounded by the techniques that farmers and cities have developed to get around such water shortages: When rivers run low, they can tap into deep aquifers or pump water from hundreds of miles away. All of which raises a tough question for a technologically advanced country like ours. If we don’t think we need the Rio Grande for its water, are we willing to save it for its own sake?

The Rio Grande is so long that when Europeans first arrived they didn’t realize it was all the same, roiling body of water. It sustained tens of thousands of Native Americans: The Pueblo people populated the basin to the north, while tribes such as the Manso lived easily off the fish, ducks and bounty of the middle river, according to accounts by Franciscan monks in 1598 who accompanied the conquistador Juan de Oñate when his expedition forded the river.