English: The grand Colorado River once flowed freely from its source in the central Rocky Mountains in the U.S. state of Colorado through about 1,450 miles (2,330 km) of arid, spectacular scenery across five states before spilling into the northern Gulf of California. Over time, however, the river’s water has proven so essential to human life and livelihoods that it has been siphoned off for crop irrigation and for residential use. Only about 10 percent of all water that flows into the Colorado River actually makes it into Mexico. Once in Mexico, most of those remnants are also used for agriculture or drinking water.

The harnessing of the Colorado transformed the Colorado River Delta. Once filled with lush marshland and many braided channels, the Delta now has diminished to sandy mudflats and scattered bits of marshland. The former rich wetland and riparian ecosystem contrasted strongly against the arid desert and served as an oasis, supporting cottonwood and willow and created breeding grounds for a large number of native species. With the loss of the Colorado’s water, invasives moved in while population of natives dropped steeply.

A joint effort between Mexico and the United States brings some hope to save some of the remaining critical ecosystems once found so richly along the Colorado River Delta. The Colorado River bi-national agreement permitted a pulse flow of water from Morelos Dam in 2014 that brought water once again to the Delta. Even this brief flow helped encourage growth of trees and increased nesting bird populations. The current agreement brought a flow of water measuring 35,000 acre-feet (11.4 billion gallons) through the river to reach the Delta from May 1 to October 11, 2021. This annual life-enhancing baptism, which will occur through 2026, is expected to help restore parts of the Delta and support habitat for threatened species.

On November 4, 2021, the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the Colorado River Delta from the Salton Sea to the Gulf of California. Patchworks of green appear at every location where water flows through the river or where water can be diverted to support agriculture. The orange-tinted sands of the Sonoran Desert can be seen in the east while bright white salt flats sit on the western banks of the Delta. A few areas of dark blue along the Delta are likely pools created by the flow emitted during the summer and early fall of this year.