Editing Potomac River (section)

===Water supply and water quality===
An average of approximately {{convert|486|e6USgal|m3}} of water is [[#cnote AQU|withdrawn daily from the Potomac in the Washington area]] for [[water supply]], providing about 78 percent of the region's total water usage, this amount includes approximately 80 percent of the drinking water consumed by the region's estimated 6.1 million residents.<ref name="basin-facts"/><ref>{{cite web |url=https://www.census.gov/content/dam/Census/newsroom/releases/2016/cb16-cn43_table_6.pdf |title=The 10 Most Populous Metro Areas : July 1, 2015 |date=July 2015 |website=www.census.gov |publisher=US Census Bureau |access-date=April 9, 2019 |archive-date=November 4, 2020 |archive-url=https://web.archive.org/web/20201104162440/https://www.census.gov/content/dam/Census/newsroom/releases/2016/cb16-cn43_table_6.pdf |url-status=live}}</ref>

[[File:The Potomac River surges over Chain Bridge during 1936 Flood 19 March 1936.jpg|thumb|The Potomac River surges over the deck of [[Chain Bridge (Potomac River)|Chain Bridge]] during the [[Pittsburgh Flood of 1936#Effects in other areas|historic 1936 flood]]. The bridge was so severely damaged by the raging water, and the debris it carried, that its superstructure had to be re-built; the new bridge was opened to traffic in 1939. (This photograph was taken from a vantage point on [[Virginia State Route 120|Glebe Road]] in Arlington County, Virginia. The houses on the bluffs in the background are located on the [[The Palisades, Washington, D.C.|Potomac Palisades]] of Washington, DC.)]]

As a result of damaging floods in 1936 and 1937,<ref name="1936Flood" /> the [[United States Army Corps of Engineers|Army Corps of Engineers]] proposed the [[Potomac River basin reservoir projects]], a series of dams that were intended to regulate the river and to provide a more reliable water supply. One dam was to be built at Little Falls, just north of Washington, backing its pool up to Great Falls. Just above Great Falls, the much larger [[Seneca Dam]] was proposed whose reservoir would extend to Harpers Ferry.<ref name="ffls1">{{cite news |url=https://news.google.com/newspapers?nid=1298&dat=19631204&id=cuQPAAAAIBAJ&pg=5587,5390295 |title=Potomac Dam Is Opposed By Virginians |last=Carey |first=Frank |date=December 4, 1963 |publisher=Fredericksburg Free-Lance Star |access-date=2009-11-13}}</ref> Several other dams were proposed for the Potomac and its tributaries.
{| class="wikitable mw-collapsible mw-collapsed" style="margin:auto;"
! style="border-width:4px; background:azure;"|Dams on the Potomac River&nbsp;
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<blockquote>
'''Operational'''
*[[Little Falls Dam (Potomac River)]] aka Brookmont Dam (at C&O Canal milepost 5.6, upstream of Chain Bridge)
*[[Washington Aqueduct|Potomac Aqueduct Dam]] (at C&O Canal milepost 17.5, upstream of Great Falls)
*[[Power Plant and Dam No. 4|C&O Feeder Dam No. 4]] (at C&O Canal milepost 84, downstream of Williamsport, MD)
*[[Power Plant and Dam No. 5 (Potomac River)|Honeywood Dam]] aka C&O Feeder Dam No. 5 (at C&O Canal milepost 106, upstream of Williamsport, MD)
*[[Cumberland Dam]] aka Feeder Dam No. 8 (on North Branch of Potomac River, 40 miles downstream of Fairfax Stone)
*[[Jennings Randolph Lake|Jennings Randolph Dam]] (on North Branch of the Potomac River, 27 miles downstream of Fairfax Stone)

'''Non-Operational'''
*[https://www.canaltrust.org/discoverypoi/feeder-dam-1/ C&O Feeder Dam No. 1] (C&O Canal milepost 5.6, upstream of Chain Bridge near Lock 6; associated with [[Little Falls Canal|Little Falls Skirting Canal]] [http://www.riverexplorer.com/details.php?id=531] )
*[http://www.riverexplorer.com/details.php?id=615 Seneca Dam] aka C&O Feeder Dam No. 2 (at C&O Canal milepost 22, near Violette's Lock)
*[http://www.riverexplorer.com/details.php?id=1304 Armory Dam] aka C&O Feeder Dam No. 3 (at C&O Canal milepost 62, upstream of Harpers Ferry, WV)<ref>{{cite web |url=http://www.candocanal.org/articles/engineering-Dam3-HF.pdf |title=Canal Engineering from Dam 3 to Harpers Ferry |last=Grey |first=Karen |date=March 2018 |website=candocanal.org |publisher='Along the Towpath', C&O Canal Association |access-date=16 March 2019 |archive-date=May 22, 2020 |archive-url=https://web.archive.org/web/20200522225632/http://www.candocanal.org/articles/engineering-Dam3-HF.pdf |url-status=live}}</ref>
*[http://candocanal.org/articles/2014-Dam6.pdf C&O Feeder Dam No. 6] {{Webarchive|url=https://web.archive.org/web/20200831231815/http://candocanal.org/articles/2014-Dam6.pdf |date=August 31, 2020 }} (at C&O Canal milepost 134, west of Hancock, MD)<ref>{{cite web |url=http://www.candocanal.org/level51.html |title=Level 51 (Dam #6) |last=Holdsworth |first=Bill |date=April 2013 |website=candocanal.org |publisher=C&O Canal Association |access-date=16 March 2019 |archive-date=June 23, 2016 |archive-url=https://web.archive.org/web/20160623024048/http://www.candocanal.org/level51.html |url-status=live}}</ref>

'''Planned, but never built'''
*C&O Feeder Dam No. 7 and Guard Lock No. 7 were proposed to be located near milepost 164, close to the mouth of the South Branch of the Potomac, but were never built due to financial considerations.<ref>{{cite web |url=https://www.nps.gov/parkhistory/online_books/choh/unrau_hrs.pdf |title=Historical Resource Study: Chesapeake & Ohio Canal |last=Unrau |first=Harland D. |date=August 2007 |publisher=US Department of the Interior, National Park Service |pages=208; 470 |access-date=16 March 2019 |archive-date=July 14, 2015 |archive-url=https://web.archive.org/web/20150714091213/http://www.nps.gov/parkhistory/online_books/choh/unrau_hrs.pdf |url-status=live}}</ref>
</blockquote>
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When detailed studies were issued by the Corps in the 1950s, they met sustained opposition, led by [[U.S. Supreme Court]] Justice [[William O. Douglas]], resulting in the plans' abandonment.<ref>{{cite news |url=https://www.washingtonpost.com/ac2/wp-dyn?pagename=article&node=&contentId=A13425-2002May1 |archive-url=https://web.archive.org/web/20020916051041/http://www.washingtonpost.com/ac2/wp-dyn?contentId=A13425-2002May1&node=&pagename=article |url-status=dead |archive-date=September 16, 2002 |title=America's River |author=Joel Achenbach |newspaper=The Washington Post |date=May 5, 2002 |pages=W12}}</ref> The only dam project that did get built was [[Jennings Randolph Lake]] on the North Branch.<ref>{{cite web |url=https://www.nab.usace.army.mil/portals/63/docs/factsheets/fy15_factsheets/md-wv-jenningsrandolphlake-om.pdf |title=Jennings Randolph Lake, MD & WV |date=February 2015 |website=www.nab.usace.army.mil |publisher=USACE (United States Corps of Engineers) |access-date=April 5, 2019 |archive-date=September 28, 2020 |archive-url=https://web.archive.org/web/20200928184024/https://www.nab.usace.army.mil/portals/63/docs/factsheets/fy15_factsheets/md-wv-jenningsrandolphlake-om.pdf |url-status=live}}</ref>
The Corps built a supplementary water intake for the Washington Aqueduct at Little Falls in 1959.<ref name="Scott">Scott, Pamela (2007), [http://140.194.76.129/publications/eng-pamphlets/ep870-1-67/toc.htm "Capital Engineers: The U.S. Army Corps of Engineers in the Development of Washington, D.C., 1790–2004."] {{webarchive|url=https://web.archive.org/web/20120226045246/http://140.194.76.129/publications/eng-pamphlets/ep870-1-67/toc.htm |date=February 26, 2012 }} (Washington, DC: U.S. Army Corps of Engineers.) Publication No. EP 870-1-67. p. 256.</ref>

In 1940 [[United States Congress|Congress]] passed a law authorizing the creation of an [[interstate compact]] to coordinate water quality management among states in the Potomac basin. Maryland, West Virginia, Pennsylvania, Virginia, and the District of Columbia agreed to establish the [[Interstate Commission on the Potomac River Basin]]. The compact was amended in 1970 to include coordination of water supply issues and land use issues related to water quality.<ref name="ICPRB timeline">ICPRB. [http://www.potomacriver.org/cms/index.php?option=com_content&view=article&id=96&catid=39&Itemid=57 "Potomac Timeline."] {{webarchive|url=https://web.archive.org/web/20110105161359/http://www.potomacriver.org/cms/index.php?option=com_content&view=article&id=96&catid=39&Itemid=57 |date=January 5, 2011 }} Updated 2008-04-15.</ref>
[[File:Potomac green water.JPG|right|thumb|[[Eutrophication]] in the Potomac River is evident from this bright green water in Washington, D.C., caused by a dense bloom of [[cyanobacteria]], April 2012.]]
Beginning in the 19th century, with increasing [[mining]] and [[agriculture]] upstream and urban [[sewage]] and [[Surface runoff|runoff]] downstream, the [[water quality]] of the Potomac River deteriorated. This created conditions of severe [[eutrophication]]. It is said that President [[Abraham Lincoln]] used to escape to the highlands on summer nights to escape the river's stench. In the 1960s, with dense green [[algae|algal]] blooms covering the river's surface, President [[Lyndon Johnson]] declared the river "a national disgrace" and set in motion a long-term effort to reduce [[water pollution|pollution]] from [[sewage]] and restore the beauty and ecology of this historic river. One of the significant pollution control projects at the time was the expansion of the [[Blue Plains Advanced Wastewater Treatment Plant]], which serves Washington and several surrounding communities.<ref>District of Columbia Water and Sewer Authority. Washington, DC. [http://www.dcwater.com/about/gen_overview.cfm "History of Blue Plains Wastewater Treatment Plant."] {{webarchive|url=https://web.archive.org/web/20150317131913/http://www.dcwater.com/about/gen_overview.cfm |date=March 17, 2015 }} Accessed 2010-09-28.</ref> Enactment of the 1972 [[Clean Water Act]] led to construction or expansion of additional [[sewage treatment]] plants in the Potomac watershed. Controls on [[phosphorus]], one of the principal contributors to eutrophication, were implemented in the 1980s, through sewage plant upgrades and restrictions on phosphorus in detergents.<ref name="ICPRB timeline" />

By the end of the 20th century, notable success had been achieved, as massive algal blooms vanished and recreational fishing and boating rebounded. Still, the aquatic [[habitat (ecology)|habitat]] of the Potomac River and its tributaries remain vulnerable to eutrophication, [[heavy metals]], [[pesticide]]s and other toxic chemicals, over-fishing, [[Alien (biology)|alien species]], and [[pathogen]]s associated with [[fecal coliform]] [[bacteria]] and [[shellfish]] diseases. In 2005 two federal agencies, the [[US Geological Survey]] and the [[Fish and Wildlife Service]], began to identify fish in the Potomac and tributaries that exhibited "intersex" characteristics, as a result of [[Endocrine disruptor|endocrine disruption]] caused by some form of pollution.<ref>U.S. Fish and Wildlife Service. Annapolis, MD (2009). [http://www.fws.gov/chesapeakebay/pdf/endocrine.pdf "Intersex fish: Endocrine disruption in smallmouth bass."] {{webarchive|url=https://web.archive.org/web/20160303192520/http://www.fws.gov/chesapeakebay/pdf/endocrine.pdf |date=March 3, 2016 }}</ref>

On November 13, 2007, the Potomac Conservancy, an environmental group, issued the river a grade of "D-plus", citing high levels of pollution and the reports of "[[intersex]]" fish.<ref>{{cite news |last=Fahrenthold |first=David A. |title=Potomac Recovery Deemed At Risk |newspaper=The Washington Post |date=November 13, 2007 |url=https://www.washingtonpost.com/wp-dyn/content/article/2007/11/12/AR2007111201814.html |access-date=2007-11-13 |url-status=live |archive-url=https://web.archive.org/web/20110701174301/http://www.washingtonpost.com/wp-dyn/content/article/2007/11/12/AR2007111201814.html |archive-date=July 1, 2011}}</ref> Since then, the river has improved with a reduction in nutrient runoff, return of fish populations, and land protection along the river. As a result, the same group issued a grade of "B" for 2017 and 2018.<ref>{{cite web |url=http://www.potomacreportcard.org/ |title=Potomac Report Card |publisher=Potomac Conservancy |date=28 March 2018 |access-date=26 March 2019 |archive-date=November 12, 2020 |archive-url=https://web.archive.org/web/20201112015940/https://www.potomacreportcard.org/ |url-status=live}}</ref> In March 2019, the [[Potomac Riverkeeper|Potomac Riverkeeper Network]] launched a laboratory boat dubbed the "Sea Dog", which will be monitoring water quality in the Potomac and providing reports to the public on a weekly basis;<ref>{{cite news|url=https://www.washingtonpost.com/local/taking-a-swim-in-the-potomac-weekly-readings-will-reveal-water-quality-and-bacteria-levels/2019/03/19/fa173378-4a71-11e9-b79a-961983b7e0cd_story.html|author-last1=Lang|author-first1=Marissa J. |title=Taking a swim in the Potomac? Weekly readings will reveal water quality and bacteria levels|archive-url=https://web.archive.org/web/20200908021241/https://www.washingtonpost.com/local/taking-a-swim-in-the-potomac-weekly-readings-will-reveal-water-quality-and-bacteria-levels/2019/03/19/fa173378-4a71-11e9-b79a-961983b7e0cd_story.html|archive-date=September 8, 2020|date=2019-03-30|access-date=2019-03-30}}</ref> in that same month, the catching near [[Fletcher's Cove|Fletcher's Boat House]] of a [[Striped Bass]] estimated to weigh {{convert|35|lb|kg|abbr=on}} was seen as a further indicator of the continuing improvement in the health of the river.<ref>[https://wtop.com/local/2019/03/need-a-bigger-boat-35-pound-bass-caught-on-the-potomac-river/ "Need a bigger boat: 35-pound bass caught on the Potomac River"] {{Webarchive|url=https://web.archive.org/web/20190403174718/https://wtop.com/local/2019/03/need-a-bigger-boat-35-pound-bass-caught-on-the-potomac-river/ |date=April 3, 2019 }}. ''Washington Post''. 2019-04-03. Accessed: 2019-04-03.</ref>
{| class="wikitable" style="width:500px; margin:auto;"
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! colspan="8" style="background:azure;"|Top Ten Historic Crests of the Potomac River, 1877–2017
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! {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/Kitzmiller.pdf | Kitzmiller}}
| align=center | {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/Hancock.pdf | Hancock}}
! {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/WilliamsportPot.pdf | Williamsport}}
| align=center |{{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/Shepherdstown.pdf| Shepherdstown}}
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| {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/HarpersFerry.pdf | Harpers Ferry}}
! align=center | {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/PointofRocks.pdf | Point of Rocks}} 
| align=center | {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/LittleFallsMD.pdf | Little Falls}}
! {{Plainlink |https://www.weather.gov/media/marfc/Top20/POT/WisconsinAve.pdf | Georgetown}}
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| colspan="8" style="text-align:center; background:white;"|Source: [[National Weather Service]]
|}