Editing Colorado River (section)

===Impacts of development===
[[File:20230522 Colorado River water usage - livestock crops etc.svg |thumb |Most of the Colorado River basin water used by humans is used to grow feed for livestock—more than four times the amount used for crops for direct human consumption.<ref name=NYTimes_20230522>{{cite news |last1=Shao |first1=Elena |title=The Colorado River Is Shrinking. See What's Using All the Water. |url=https://www.nytimes.com/interactive/2023/05/22/climate/colorado-river-water.html |work=The New York Times |date=May 22, 2023 |archive-url=https://web.archive.org/web/20230523164140/https://www.nytimes.com/interactive/2023/05/22/climate/colorado-river-water.html |archive-date=May 23, 2023 |url-status=live }} Shao cites {{cite journal |last1=Richter |first1=Brian D. |last2=Bartak |first2=Dominique |last3=Cladwell |first3=Peter |last4=Davis |first4=Kyle Frankel |last5=Debaere |first5=Peter |last6=Hoekstra |first6=Arjen Y. |last7=Li |first7=Tianshu |last8=Marston |first8=Landon |last9=McManamay |first9=Ryan |last10=Mekonnen |first10=Mesfin |last11=Ruddell |first11=Benjamin L. |last12=Rushforth |first12=Richard R. |last13=Troy |first13=Tara J. |display-authors=4 |title=Water scarcity and fish imperilment driven by beef production |journal=Nature Sustainability |date=April 2020 |volume=3 |issue=4 |pages=319–328 |doi=10.1038/s41893-020-0483-z |bibcode=2020NatSu...3..319R |s2cid=211730442 |url=https://www.nature.com/articles/s41893-020-0483-z.epdf |access-date=May 24, 2023 |archive-date=May 24, 2023 |archive-url=https://web.archive.org/web/20230524064142/https://www.nature.com/articles/s41893-020-0483-z.epdf |url-status=live }}</ref>]]
[[File:Horseshoebend smt.jpg|thumb|right|alt=View of a narrow green river flowing between high, reddish-brown cliffs|The Colorado was named for the reddish color caused by its natural sediment loads, but damming the river has caused it to acquire a clear green hue as seen here in lower Glen Canyon.]]
Historically, the Colorado [[Sediment transport|transported]] from {{convert|85|to|100|e6ST|t}} of sediment or silt to the Gulf of California each year – second only to the Mississippi among North American rivers.{{sfn|Gupta|p=200|2007}} This sediment nourished wetlands and riparian areas along the river's lower course, particularly in its {{convert|3000|mi2|km2|adj=on}} delta, once the largest desert estuary on the continent.<ref>{{cite web |url=https://www.npr.org/sections/pictureshow/2011/07/15/137821595/why-the-colorado-river-stopped-flowing?singlePage=false |title=Why The Colorado River Stopped Flowing |publisher=National Public Radio |date=July 14, 2011 |access-date=February 20, 2012 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819072827/https://www.npr.org/sections/pictureshow/2011/07/15/137821595/why-the-colorado-river-stopped-flowing?singlePage=false |url-status=live }}</ref> Currently, the majority of sediments carried by the Colorado River are deposited at the upper end of Lake Powell, and most of the remainder ends up in Lake Mead. Various estimates place the time it would take for Powell to completely fill with silt at 300 to 700 years. Dams trapping sediment not only pose damage to river habitat but also threaten future operations of the Colorado River reservoir system.<ref>{{cite web |author=Weisheit, John |url=http://www.riverguides.org/Confluence/27/27SedimentWeisheit.pdf |title=A Colorado River Sediment Inventory |publisher=Colorado Plateau River Guides |access-date=February 20, 2012 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819071316/http://www.riverguides.org/Confluence/27/27SedimentWeisheit.pdf |url-status=live }}</ref>

Reduction in flow caused by dams, diversions, water for thermoelectric power stations,<ref>{{cite web |title=Colorado River Basin |url=http://www.coriverbasin.org/ |publisher=coriverbasin.org |access-date=May 20, 2013 |archive-date=May 29, 2013 |archive-url=https://web.archive.org/web/20130529184259/http://coriverbasin.org/ |url-status=live }}</ref> and [[evaporation]] losses from reservoirs – the latter of which consumes more than 15&nbsp;percent of the river's natural runoff<ref>{{cite web |url=http://www.usbr.gov/uc/library/envdocs/reports/crs/pdfs/crs962000.pdf |title=Colorado River System Consumptive Uses and Losses Report 1996–2000 |publisher=U.S. Bureau of Reclamation |archive-url=https://web.archive.org/web/20090119165100/http://www.usbr.gov/uc/library/envdocs/reports/crs/pdfs/crs962000.pdf |archive-date=January 19, 2009 |date=December 2004}}</ref>—has had severe ecological consequences in the Colorado River Delta and the Gulf of California. Historically, the delta with its large freshwater outflow and extensive salt marshes provided an important breeding ground for aquatic species in the Gulf. Today's desiccated delta, at only a fraction of its former size, no longer provides suitable habitat, and populations of fish, shrimp and sea mammals in the gulf have seen a dramatic decline.<ref name="Controversy">{{cite web |author=Davis, Eric F. |url=https://www.msu.edu/~davise16/pdf/The%20Colorado%20River%20Controversy.pdf?q=colorado-river |title=The Colorado River Controversy |publisher=Michigan State University |format=PDF |archive-url=https://web.archive.org/web/20041001045622/http://www.msu.edu/~davise16/pdf/The%20Colorado%20River%20Controversy.pdf |archive-date=October 1, 2004}}</ref> Since 1963, the only times when the Colorado River has reached the ocean have been during [[El Niño]] events in the 1980s and 1990s.<ref name="Landmark">{{cite magazine |author=Sandra Postel |url=http://newswatch.nationalgeographic.com/2013/04/05/landmark-cooperation-brings-the-colorado-river-home/ |archive-url=https://web.archive.org/web/20130407110811/http://newswatch.nationalgeographic.com/2013/04/05/landmark-cooperation-brings-the-colorado-river-home/ |url-status=dead |archive-date=April 7, 2013 |title=Landmark Cooperation Brings the Colorado River Home |magazine=[[National Geographic (magazine)|National Geographic]] |date=April 5, 2013 |access-date=May 19, 2014}}</ref>

Reduced flows have led to increases in the concentration of certain substances in the lower river that have impacted water quality. Salinity is one of the major issues and also leads to the corrosion of pipelines in agricultural and urban areas.<ref name=":0" /> The lower Colorado's salt content was about 50 parts per million (ppm) in its natural state,<ref name="Controversy"/> but by the 1960s, it had increased to well over 2000 ppm.<ref>{{cite web |author1=Oyarzabal-Tamargo, Francisco |author2=Young, Robert A. |url=http://ageconsearch.umn.edu/bitstream/32180/1/01010007.pdf |title=The Colorado River Salinity Problem: Direct Economic Damages in Mexico |publisher=University of Minnesota |date=June 1977 |access-date=February 20, 2012 |archive-date=May 14, 2013 |archive-url=https://web.archive.org/web/20130514074643/http://ageconsearch.umn.edu/bitstream/32180/1/01010007.pdf |url-status=live }}</ref> By the early 1970s, there was also serious concern about salinity caused by salts leached from local soils by irrigation drainage water, which were estimated to add {{convert|10|e6ST|t}} of excess salt to the river per year. The [[Colorado River Basin Salinity Control Program|Colorado River Basin Salinity Control Act]] was passed in 1974, mandating conservation practices including the reduction of saline drainage. The program reduced the annual load by about {{convert|1.2|e6ST|t}}, but salinity remains an ongoing issue.<ref name="CRBSCP">{{cite web |url=http://www.socalsalinity.org/pdfs/CRBSCPBriefingDocument.pdf |title=Colorado River Basin Salinity Control Program |publisher=Southern California Salinity Coalition |access-date=June 29, 2013 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304123501/http://www.socalsalinity.org/pdfs/CRBSCPBriefingDocument.pdf |url-status=dead}}</ref> In 1997, the USBR estimated that saline irrigation water caused crop damages exceeding $500&nbsp;million in the U.S. and $100&nbsp;million in Mexico. Further efforts have been made to combat the salt issue in the lower Colorado, including the construction of a [[desalination plant]] at Yuma.<ref>{{cite web |url=http://www.usbr.gov/projects/Project.jsp?proj_Name=Colorado+River+Basin+Salinity+Control+Project |title=Colorado River Basin Salinity Control Project |publisher=U.S. Bureau of Reclamation |date=April 18, 2011 |access-date=February 21, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120228054940/http://www.usbr.gov/projects/Project.jsp?proj_Name=Colorado+River+Basin+Salinity+Control+Project |archive-date=February 28, 2012}}</ref> In 2011, the seven U.S. states agreed upon a "Plan of Implementation", which aims to reduce salinity by {{convert|644000|ST|t}} per year by 2030.<ref name="CRBSCP"/> In 2013, the Bureau of Reclamation estimated that around $32&nbsp;million was spent each year to prevent around 1.2&nbsp;million tons of salt from entering and damaging the Colorado River.<ref name=":0">{{Cite web |url=https://watershed.ucdavis.edu/education/classes/files/content/page/6%20Morford-Colorado_Basin_Salinity.pdf |title=Salinity in the Colorado River Basin |last=Morford |first=Scott |website=UC Davis Center for Watershed Sciences |access-date=February 23, 2017 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819071325/https://watershed.ucdavis.edu/education/classes/files/content/page/6%20Morford-Colorado_Basin_Salinity.pdf |url-status=dead}}</ref>

Agricultural runoff containing pesticide residues has also been concentrated in the lower river in greater amounts. This has led to fish kills; six of these events were recorded between 1964 and 1968 alone.<ref>{{cite web |url=http://nepis.epa.gov/Exe/ZyNET.exe/91008B82.TXT?ZyActionD=ZyDocument&Client=EPA&Index=Prior+to+1976&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C70thru75%5CTxt%5C00000008%5C91008B82.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL |title=Technical Report: Pesticides in the Lower Colorado River |publisher=U.S. Environmental Protection Agency |work=Surveillance and Analysis Division, Report No. 002–73 |date=April 1973 |access-date=June 29, 2013 |archive-date=August 13, 2020 |archive-url=https://web.archive.org/web/20200813120226/https://nepis.epa.gov/Exe/ZyNET.exe/91008B82.TXT?ZyActionD=ZyDocument&Client=EPA&Index=Prior+to+1976&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C70thru75%5CTxt%5C00000008%5C91008B82.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=p%7Cf&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL |url-status=live }}</ref> The pesticide issue is even greater in streams and water bodies near agricultural lands irrigated by the [[Imperial Irrigation District]] with Colorado River water. In the Imperial Valley, Colorado River water used for irrigation overflows into the [[New River (Mexico-United States)|New]] and Alamo rivers and into the Salton Sea. Both rivers and the sea are among the most polluted bodies of water in the United States, posing dangers not only to aquatic life but to contact by humans and migrating birds.<ref>{{cite web |url=http://www.waterboards.ca.gov/coloradoriver/about_us/about_region7.shtml |title=About Region 7 |publisher=California Environmental Protection Agency |work=Colorado River Basin Regional Water Quality Control Board |access-date=June 29, 2011 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819071740/https://www.waterboards.ca.gov/coloradoriver/about_us/about_region7.html |url-status=live }}</ref><ref>{{cite web |author=Polakovic, Gary |url=http://www.sci.sdsu.edu/salton/ASeaInTrouble.html |title=A Sea in Trouble |publisher=San Diego State University |work=The Press-Enterprise |access-date=June 29, 2011 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819071730/http://www.sci.sdsu.edu/salton/ASeaInTrouble.html |url-status=live }}</ref> Pollution from agricultural runoff is not limited to the lower river; the issue is also significant in upstream reaches such as Colorado's Grand Valley, also a major center of irrigated agriculture.<ref>{{cite web |author1=Bauch, Nancy J. |author2=Spahr, Norman E. |url=http://pubs.usgs.gov/wri/wri00-4005/pdf/wrir00-4005.pdf |title=Pesticides in Surface Waters of the Upper Colorado River Basin, Colorado, 1996–98 |publisher=U.S. Geological Survey |work=Water-Resources Investigation Report 00-4005 |year=2000 |access-date=June 29, 2013 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819072006/https://pubs.usgs.gov/wri/wri00-4005/pdf/wrir00-4005.pdf |url-status=live }}</ref>

Large dams such as Hoover and Glen Canyon typically release water from lower levels of their reservoirs, resulting in stable and relatively cold year-round temperatures in long reaches of the river. The Colorado's average temperature once ranged from {{convert|85|F|C}} at the height of summer to near freezing in winter, but modern flows through the Grand Canyon, for example, rarely deviate significantly from {{convert|46|F|C}}.<ref>{{cite web |url=http://www.glencanyon.org/glen_canyon/grand-canyon |title=Grand Canyon |publisher=Glen Canyon Institute |access-date=February 21, 2012 |archive-url=https://web.archive.org/web/20120224091339/http://www.glencanyon.org/glen_canyon/grand-canyon |archive-date=February 24, 2012 |url-status=dead}}</ref> Changes in temperature regime have caused declines of native fish populations, and stable flows have enabled increased vegetation growth, obstructing riverside habitat.<ref>{{cite journal |title=Temperature Effects of Hypolimnial-Release Dams on Early Life Stages of Colorado River Basin Big-River Fishes |journal=Copeia |volume=2000 |date=May 8, 2000 |author1=Clarkson, Robert W. |author2=Childs, Michael R. |issue=2 |pages=402–412 |doi=10.1643/0045-8511(2000)000[0402:teohrd]2.0.co;2 |s2cid=85964507}}</ref> These flow patterns have also made the Colorado more dangerous to recreational boaters; people are more likely to die of hypothermia in the colder water, and the general lack of flooding allows rockslides to build up, making the river more difficult to navigate.{{sfn|Ghiglieri|Myers|2001|pp=194–214}}

====Minute 319====
In the 21st&nbsp;century, there has been renewed interest in restoring a limited water flow to the delta. In November 2012, the U.S. and Mexico reached an agreement, known as Minute 319, permitting Mexico storage of its water allotment in U.S. reservoirs during wet years, thus increasing the efficiency with which the water can be used. In addition to renovating irrigation canals in the Mexicali Valley to reduce leakage, this will make about {{convert|45000|acre.ft|m3}} per year available for release to the delta on average. The water will be used to provide both an annual base flow and a spring "pulse flow" to mimic the river's original snowmelt-driven regime.<ref>{{cite news |title=Colorado River Agreement to Help Restore Vanished Wetlands in Mexico |url=http://pri.org/stories/2012-11-26/colorado-river-agreement-help-restore-vanished-wetlands-mexico |first1=Jason |last1=Margolis |first2=Lisa |last2=Mullins |work=The World |publisher=Public Radio International |date=November 26, 2012 |access-date=November 2, 2013 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819072354/https://www.pri.org/stories/2012-11-26/colorado-river-agreement-help-restore-vanished-wetlands-mexico |url-status=live }}</ref><ref>{{cite web |url=https://www.watereducation.org/userfiles/RiverReport_Winter13_web.pdf |title=Minute 319: Building on the Past to Provide for the Future |publisher=Water Education Foundation |work=River Report |date=2012–2013 |access-date=June 29, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20140501135538/https://www.watereducation.org/userfiles/RiverReport_Winter13_web.pdf |archive-date=May 1, 2014}}</ref> The first pulse flow, an eight-week release of {{convert|105000|acre.ft|m3}}, was initiated on March 21, 2014, with the aim of revitalising {{convert|2350|acre|hectare}} of [[wetland]].<ref name="Pulse">{{cite magazine |title=Huge water pulse to bring Colorado river back from dead |url=https://www.newscientist.com/article/mg22129602.800-huge-water-pulse-to-bring-colorado-river-back-from-dead.html#.U3pqrijYJJQ |first=Hal |last=Hodson |magazine=New Scientist |date=March 12, 2014 |access-date=May 19, 2014 |archive-date=August 28, 2021 |archive-url=https://archive.today/20210828120731/https://www.newscientist.com/article/mg22129602-800-huge-water-pulse-to-bring-colorado-river-back-from-dead/?ignored=irrelevant%23.U3pqrijYJJQ |url-status=live }}</ref> This pulse reached the sea on May 16, 2014, marking the first time in 16 years that any water from the Colorado flowed into the ocean, and was hailed as "an experiment of historic political and ecological significance" and a landmark in U.S.–Mexican cooperation in conservation.<ref name="Sacred"/><ref>{{cite magazine |title=Colorado river reaches sea for first time in decades |url=https://www.newscientist.com/article/dn25587#.U3pqsyjYJJQ |first=Hal |last=Hodson |magazine=New Scientist |date=May 19, 2014 |access-date=May 19, 2014 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819071944/https://www.newscientist.com/article/dn25587-colorado-river-reaches-sea-for-first-time-in-decades/#.U3pqsyjYJJQ |url-status=live }}</ref><ref>{{cite news |last=Galvan |first=Astrid |date=May 19, 2014 |title=Colorado River Reaches Gulf |publisher=ABC and Associated Press |url=https://abcnews.go.com/US/wireStory/colorado-river-reaches-gulf-23753772 |url-status=dead |access-date=May 19, 2014 |archive-url=https://web.archive.org/web/20140519073738/https://abcnews.go.com/US/wireStory/colorado-river-reaches-gulf-23753772 |archive-date=May 19, 2014}}</ref> The pulse will be followed by the steady release of {{convert|52000|acre.ft|m3}} over the following three years, just a small fraction of its average flow before damming.<ref name="Pulse"/>{{needs update|date=February 2021}}