The Missing Colorado River Delta: Rivers, Borders, and Maps

Screenshot of the USGS Streamers mapping website

Water flows downhill, and you wouldn’t think that rivers would stop for political boundaries, not even when national borders intersect a river channel’s natural course.  The Mekong flows through China, Laos, Burma, Thailand, Vietnam, and Cambodia before it drains into the South China Sea.  The Nile watershed includes Ethiopia, Uganda, South Sudan, Sudan, and Egypt, where its delta enters the Mediterranean Sea.

And then there’s the Colorado River (see map), which starts in the Rocky Mountain peaks of the United States, and flows into Mexico, where it empties into the Upper Sea of Cortez.  Except that usually it doesn’t:  the unsustainable demand for water from the river—so great that it exceeds the river’s supply—has for the last decade essentially desiccated the Colorado’s last hundred miles.  The need to restore flows and habitat in the Colorado River Delta is a topic I’ve written on before, and it’s very exciting to see the United States and Mexico cooperating to do just that.

So it was with considerable surprise that I looked at a new product from the United States Geologic Survey (USGS), their Streamer tool that shows how rivers run from anywhere in the United States.  USGS’s intent—to illustrate watersheds and inform us about how our favorite rivers connect to a larger landscape—is commendable.  But Streamer does not show rivers where they cross the United States border, and that is a problem.

On the Streamers website, I pointed to the headwaters of the Colorado River in Rocky Mountain National Park and clicked on “trace downstream” to see the river’s route.  What I saw was a river course stopping abruptly at the Mexican border.  In many ways this mapping flaw illustrates why the Colorado’s delta was allowed to deteriorate so badly:  a federal government that sees borders as the limit of its responsibility is one that will not manage holistically. (See stories from the Colorado River Delta.)

US Bureau of Reclamation's 1974 map of the Colorado River
U.S. Bureau of Reclamation’s 1974 map of the Colorado River

Until 2012, the United States’ management of the Colorado River was based on exactly this view:  whatever happened to the Colorado once it entered Mexico was beyond U.S. jurisdiction, and thus was excluded from consideration in river management.  And in fact for years, the U.S. Bureau of Reclamation, the federal agency managing the Colorado, used maps showing the Colorado stopping at the border.  Thankfully some of their recent maps correct this, and moreover the U.S. and Mexico have agreed to work together on restoring the environment in the Colorado’s delta.

A final note of surprise at the Streamers map is that it shows the Colorado River draining into the Salton Sea.  That’s actually a fairly accurate depiction:  In 2012 the Imperial Irrigation District diverted some 2.9 million acre-feet, more than 20 percent of the Colorado’s annual average flow and perhaps as much as 40 percent of the river’s estimated flow that year.  This diversion empties the Colorado of the vast majority of flow left in the channel by the time it gets down below Parker Dam.  And close to 1 million acre-feet—7 percent of the river’s flow—drained from the Imperial Irrigation District into the Salton Sea, which is several orders of magnitude more water than flowed into the Colorado River Delta last year.

Perhaps USGS gets kudos for showing the actual flows—diverted into canals that take water out of the river for use elsewhere.  But then where are the diversions into California’s Colorado River aqueduct, about 7 percent of the river?  And the Central Arizona Project, about 12 percent?  Don’t those canals also drain the Colorado?

Mapping streamflow is informative and has great value.  USGS gets credit for a new and innovative tool, and I don’t doubt there are obstacles—both technical and political—to mapping rivers outside the borders of the United States.  But clipping rivers at international boundaries does a disservice to USGS’s viewers, and does not reflect the new, binational cooperation on the Colorado and elsewhere.  USGS could help the cause of healthy rivers by including their full courses, borders notwithstanding.


Jennifer Pitt is the Colorado River Project Director for Environmental Defense Fund. She works with Colorado River water users throughout the Colorado River basin—including seven states in the United States and two in Mexico—to develop practical programs to restore river habitats and to dedicate water to environmental resources. She has worked as a park ranger and a Congressional aide, and has a Masters degree in Environmental Studies from Yale University.
  • John Patrick Mackey

    It’s so important to improve relations with our Mexican neighbors. Let the Imperial Valley reach out to the mayor of Mexicali, with a view toward restoring the Delta & Laguna Salada. Mexicali, the Baja State capital, has One-Million residents. The wind around there usually comes from the north, meaning that a dried-up Salton Sea bed will fuel toxic dust storms throughout the Mexicali Valley. My solution = a PIPE from the Gulf of California via the 67-mile route of The New River.

  • Wayne Lambert

    The name of the agency, which was founded in 1879 and is one of the oldest federal agencies to still retain its original name, is U. S. Geological Survey.

  • Kevin

    A poor record of river stewardship!

  • John Gottes

    Ms Jennifer: Is odd the USGS shows the Salton Basin as part of the Colorado River Basin. Historically, the Colorado did flow into the basin, but certainly not as far north as Palm Springs. Perhaps the USGS was intending to show where the waters are diverted to? They do include the Central Arizona Project (all of AZ is included in the Basin) but your right, the USGS doesn’t include the diversions into CA’s Colorado River Aqueduct . . . Not sure why they would include some diversions, and not others.
    I would guess they were intending to show just the natural basin, and were a bit imprecise with the drawing (a rare mistake for the USGS).

    The USGS maps don’t include the delta in Mexico because they’re funding does not extend to foreign countries. Their mandate is to map the US.

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