Editing Great Lakes (section)

===Water levels===
The lakes were originally fed by both precipitation and [[meltwater]] from glaciers which are no longer present. In modern times, only about 1% of volume per year is "new" water, originating from rivers, precipitation, and groundwater springs. In the post-glacial period, [[evaporation]], and drainage have generally been balanced, making the levels of the lakes relatively constant.<ref name=Grady/>

Intensive [[World population|human population]] growth began in the region in the 20th century and continues today.<ref name=Grady/> At least two human water use activities have been identified as having the potential to affect the lakes' levels: diversion (the transfer of water to other watersheds) and consumption (substantially done today by the use of lake water to power and cool electric generation plants, resulting in evaporation).<ref>{{cite web |url = http://www.epa.gov/glnpo/solec/index.html |title = State of the Great Lakes 2009 Highlights |publisher = [[Environment Canada]] and Environmental Protection Agency |access-date = July 7, 2013 |pages = 7–8 }}</ref> Outflows through the Chicago Sanitary and Ship Canal is more than balanced by artificial inflows via the [[Ogoki River]] and Long Lake/[[Kenogami River]] diversions.<ref>{{cite web |title = An Overview of Great Lakes Diversions |url = https://ijc.org/en/lsbc/watershed/great-lakes-diversions |publisher = [[International Joint Commission]] |date = May 14, 2020 |access-date = September 29, 2021 }}</ref> Fluctuation of the water levels in the lakes has been observed since records began in 1918.<ref name="auto">{{cite web |url = https://lre-wm.usace.army.mil/ForecastData/GLBasinConditions/LTA-GLWL-Graph.pdf |archive-url = https://web.archive.org/web/20190711121842/http://lre-wm.usace.army.mil/ForecastData/GLBasinConditions/LTA-GLWL-Graph.pdf |archive-date = July 11, 2019 |url-status = live |title = Great Lakes Water Levels (1918–2021) |publisher = United States Army Corps of Engineers |access-date = June 26, 2021 }}</ref> The water level of Lake Michigan–Huron had remained fairly constant over the 20th century.<ref name="BolsengaHerdendorf1993">{{cite book |last1 = Bolsenga |first1 = Stanley J. |last2 = Herdendorf |first2 = Charles E. |title = Lake Erie and Lake Saint Clair Handbook |url = https://books.google.com/books?id=nndmmFTWkVEC&pg=PA67 |year = 1993 |publisher = Wayne State University Press |isbn = 978-0-8143-2470-7 |page = 67 }}</ref> Recent lake levels include record low levels in 2013 in Lakes Superior, Erie, and Michigan-Huron,<ref name=jsonline>{{cite web |url = http://www.jsonline.com/news/wisconsin/lakes-michigan-huron-hit-record-low-level-dq8loc2-189903561.html |work = Milwaukee Journal Sentinel |title = Lakes Michigan, Huron hit record low water level |last = Egan |first = Dan |date = February 5, 2013 |access-date = June 26, 2021 }}</ref> followed by record high levels in 2020<ref>{{cite web |url = https://www.glerl.noaa.gov/data/wlevels/data/miHuronLevelsFeet.png |title = Lake Michigan-Huron Water Levels from Harbor Beach, MI - 9075014 2020 – 2021 |publisher = National Oceanic and Atmospheric Administration |access-date = June 26, 2021 }}</ref> in the same lakes. The water level in Lake Ontario has remained relatively constant in the same time period, hovering around the historical average level.<ref name="auto"/>

[[File:Great lakes water level.png|thumb|upright=1.1|Water levels of Lakes Michigan and Huron in the United States, 1918 to 2019]]

Although "true tides—changes in water level caused by the gravitational forces of the sun and moon—do occur in a semi-diurnal (twice daily) pattern", such changes are quite small and generally obscured by other forces.<ref>{{Cite web |last=US Department of Commerce |title=Do the Great Lakes have tides? |url=https://oceanservice.noaa.gov/facts/gltides.html# |access-date=2024-11-27 |website=National Oceanic and Atmospheric Administration |language=EN-US}}</ref>  The lake levels are affected primarily by changes in regional meteorology and climatology. The outflows from Lakes Superior and Ontario are regulated, while the outflows of Michigan-Huron and Erie are not regulated at all. Ontario is the most tightly regulated, with its outflow controlled by the [[Moses-Saunders Power Dam]], which explains its consistent historical levels.<ref>{{cite news |last = Armstrong |first = Leslie |title = Great Lakes Water Levels Rebound Thanks to Prolonged Winter |newspaper = Toronto Star |date = August 14, 2014 }}</ref>