For millions of years, the Rio Grande has been one of the greatest rivers of North America.In the Big Bend region, its majestic flow has helped to create a truly fantastic landscape, slowly wearing away thousands of feet of rock to produce three of North America’s most spectacular river canyons (These canyons prompted an early visitor to call the Big Bend a place “where the big river is kept in a stone box.”). In an otherwise dry and seemingly barren desert, the Rio Grande has produced a sparkling ribbon of water and lush, green vegetation teeming with fish, birds and other forms of wildlife.
Unfortunately, over the past one hundred years, the Rio Grande has changed dramatically, until today, it is little more than a shadow of its former self. Impoundment, irrigation and other human uses have reduced its flow dramatically, until it no longer floods in a natural cycle (something that is extremely important to both vegetation and wildlife), and its silt often is mingled with various pollutants. A hundred years ago, people drank from the river freely, but today, park visitors should use caution if they wade or swim in it.
Perhaps the greatest threat to the river’s overall health is its reduced and/or regulated flow. In recent decades, the construction of dams and the tremendous growth of cities, industry and agriculture along the Rio Grande have diverted huge amounts of water. Sometimes the river below El Paso is nothing more than a dry wash. Where does the water come from that flows through the park? It is mostly the Rio Conchos which originates in the mountains of Chihuahua, Mexico, and enters the channel of the Rio Grande near Presidio, Texas. This river has also been reduced due to growing agricultural and municipal use in Mexico.When this reduction is coupled with recurring, natural droughts, the results can be disastrous.
For example, by May 2003 the extreme drought of the past ten years had reduced the river’s flow to the point where, for the first time in fifty years, it actually ceased for a few weeks. Park staff noted significant areas in both Santa Elena Canyon and Mariscal Canyon where the river consisted only of stagnant pools, with no flow between them.
At least seven species of fish have now disappeared from the Rio Grande in the Big Bend area, including the American eel, the sturgeon and the Rio Grande silvery minnow. Also, at least five native mussels may be gone, since only the dead shells of three species have been found in recent years. And the Big Bend slider (a species of turtle) may soon disappear, since it is adapted only to swift water conditions.
Along with its reduced and regulated flow, the river frequently contains high levels of salts and bacteria, as well as agricultural and industrial chemicals. Such contamination affects a wide variety of species. For instance, high levels of both mercury and selenium have been detected in many of the river’s fish, in aquatic insects, and in numerous bird species that feed on aquatic organisms.
Because of the Rio Grande’s importance to the overall environmental health of the Big Bend region, Big Bend National Park cooperates with the U.S. Geologic Survey (USGS) and other agencies to monitor the river’s condition and the quality of its water. Presently, the park can measure the river’s temperature, acidity, oxygen content and salinity as often as every six hours at both Castolon and Rio Grande Village. Recent testing has shown that the river’s oxygen content and salinity can change dramatically with rises and falls in the river’s level. A slight rise in May 2002 correlated with a drop in dissolved oxygen that was severe enough to kill fish near Hot Springs.
The park’s monitoring activities have contributed to a program called the National Stream Quality Accounting Network (NASQAN). Sponsored by the USGS, this program eventually will provide important clues for determining the impact of upstream reservoirs on the river and the sources of pesticides and agricultural chemicals in its water. This in turn may be the first step in restoring at least some of the river’s natural vitality and ecological importance. Without many dramatic changes, it seems unlikely that the “big river in a stone box” will ever fully regain its former, natural role in the story of America’s Southwest.
This article by park ranger Doug Thompson originally appeared in the Fall/Winter 2003 issue of The Big Bend Paisano.
Last updated: February 24, 2015