Editing Great Lakes (section)

==Geography==
[[File:Sub-basins Great Lakes Basin.png|thumb|right|upright=1.1|A map of the Great Lakes Basin showing the five sub-basins. Left to right they are: Superior (magenta); Michigan (cyan); Huron (green); Erie (yellow); Ontario (red).]]
Though the five lakes lie in separate basins, they form a single, naturally interconnected body of fresh water, within the [[Great Lakes Basin]]. As a chain of lakes and rivers, they connect the east-central interior of North America to the Atlantic Ocean. From the interior to the outlet at the Saint Lawrence River, water flows from Superior to Huron and Michigan, southward to Erie, and finally northward to Lake Ontario. The lakes [[Drainage system (geomorphology)|drain a large watershed]] via many rivers and contain approximately 35,000 islands.<ref name="Bennett1999as">{{cite book |last=Bennett |first=Tom |title=State of the Great Lakes: 1997 Annual Report |url=https://books.google.com/books?id=uN2nhumNsiAC&pg=PA1991-IA7 |publisher=Diane Publishing |year=1999 |page=1991 |isbn=978-0-7881-4358-8}}</ref> There are also several thousand smaller lakes, often called "inland lakes", within the basin.<ref name="Likens2010at">{{cite book |last=Likens |first=Gene E. |title=Lake Ecosystem Ecology: A Global Perspective |url=https://books.google.com/books?id=OzJOqh90RuwC&pg=PA326 |publisher=Academic Press |year=2010 |page=326 |isbn=978-0-12-382003-7}}</ref>

The surface area of the five primary lakes combined is roughly equal to the size of the United Kingdom, while the surface area of the entire basin (the lakes and the land they drain) is about the size of the UK and France combined.<ref name="Grady" /> Lake Michigan is the only one of the Great Lakes that is entirely within the United States; the others form a water boundary between the United States and Canada. The lakes are divided among the jurisdictions of the Canadian province of [[Ontario]] and the U.S. states of [[Michigan]], [[Wisconsin]], [[Minnesota]], [[Illinois]], [[Indiana]], [[Ohio]], [[Pennsylvania]], and [[New York (state)|New York]]. Both the province of Ontario and the state of Michigan include in their boundaries portions of four of the lakes. The province of Ontario does not border Lake Michigan, and the state of Michigan does not border Lake Ontario. New York and Wisconsin's jurisdictions extend into two lakes, and each of the remaining states into one of the lakes.

===Bathymetry===
{| border="0" cellspacing="2" cellpadding="0" style="width:600px; font-size:smaller;"
|+ Relative elevations, average depths, maximum depths, and volumes of the Great Lakes
|-
|colspan=2|
<timeline>
ImageSize = width:595 height:250
PlotArea = width:525 height:200 left:50 bottom:15
AlignBars = justify

Period = from:-1000 till:600
TimeAxis = orientation:vertical
ScaleMajor = unit:year increment:500 start:-1000
ScaleMinor = unit:year increment:100 start:-1000

Colors =
 id:blue1 value:rgb(0.0,0.0,0.75)
 id:blue2 value:rgb(0.1,0.1,0.8)
 id:blue3 value:rgb(0.2,0.2,0.85)
 id:blue4 value:rgb(0.3,0.3,0.9)
 id:blue5 value:rgb(0.4,0.4,0.95)
 id:textinbar value:yelloworange
 id:textoutsidebar value:redorange

Define $elevation = shift:(0,15) mark:(line,textoutsidebar) textcolor:textoutsidebar
Define $avgdepth = mark:(line,textinbar) textcolor:textinbar
Define $maxdepth = shift:(0,-11) mark:(line,textoutsidebar) textcolor:textoutsidebar

PlotData=
 align:center

 bar:Superior from:-732 till:600 width:194 color:blue1
 $elevation at:600 text:"600&nbsp;ft (183&nbsp;m)"
 $avgdepth at:117 shift:(0,1) text:"483&nbsp;ft (147&nbsp;m)"
 $maxdepth at:-732 text:"1,332&nbsp;ft (406&nbsp;m)"

 bar:Michigan from:-348 till:577 width:113 color:blue5
 $elevation at:577 text:"577&nbsp;ft (176&nbsp;m)"
 $avgdepth at:298 shift:(0,2) text:"279&nbsp;ft (85&nbsp;m)"
 $maxdepth at:-348 text:"925&nbsp;ft (282&nbsp;m)"

 bar:Huron from:-173 till:577 width:101 color:blue3
 $elevation at:577 text:"577&nbsp;ft (176&nbsp;m)"
 $avgdepth at:382 shift:(0,1) text:"195&nbsp;ft (59&nbsp;m)"
 $maxdepth at:-173 text:"750&nbsp;ft (229&nbsp;m)"

 bar:Erie from:359 till:569 width:49 color:blue2
 $elevation at:569 text:"569&nbsp;ft (173&nbsp;m)"
 $avgdepth at:507 align:left shift:(30,2) text:"62&nbsp;ft (19&nbsp;m)"
 $maxdepth at:359 text:"210&nbsp;ft (64&nbsp;m)"

 bar:Ontario from:-559 till:243 width:44 color:blue4
 $elevation at:243 text:"243&nbsp;ft (74&nbsp;m)"
 $avgdepth at:-40 shift:(0,2) text:"283&nbsp;ft (86&nbsp;m)"
 $maxdepth at:-559 text:"802&nbsp;ft (244&nbsp;m)"

 align:left shift:(35,0) textcolor:green
 at:243 text:"surface~elevation"
 at:-40 text:"average~depth"
 at:-559 text:"maximum~depth"
</timeline>
|- valign=top
!align=right| Notes:
| The area of each rectangle is proportional to the volume of each lake. All measurements at Low Water Datum.
|- valign=top
!align=right| Source:
| United States Environmental Protection Agency<ref name=EPA>{{cite web |url = http://www.epa.gov/glnpo/atlas/gl-fact1.html |title = Great Lakes Atlas: Factsheet #1 |access-date = December 3, 2007 |date = March 9, 2006 |website = U.S. Environmental Protection Agency |url-status = dead |archive-url = https://web.archive.org/web/20080328170959/http://www.epa.gov/glnpo/atlas/gl-fact1.html |archive-date = March 28, 2008 }}</ref>
|}

{| class="wikitable" style="text-align:center;" cellpadding="5"
|-

!
![[Lake Erie]]
![[Lake Huron]]
![[Lake Michigan]]
![[Lake Ontario]]
![[Lake Superior]]
|-
! Surface area<ref name="EPAphysical"/>
| {{convert|9910|sqmi|km2|abbr=on|order=flip}}
| {{convert|23000|sqmi|km2|abbr=on|order=flip}}
| {{convert|22300|sqmi|km2|abbr=on|order=flip}}
| {{convert|7340|sqmi|km2|abbr=on|order=flip}}
| {{convert|31700|sqmi|km2|abbr=on|order=flip}}
|-
! Water volume<ref name="EPAphysical"/>
| {{convert|116|cumi|km3|abbr=on|order=flip}}
| {{convert|850|cumi|km3|abbr=on|order=flip}}
| {{convert|1180|cumi|km3|abbr=on|order=flip}}
| {{convert|393|cumi|km3|abbr=on|order=flip}}
| {{convert|2900|cumi|km3|abbr=on|order=flip}}
|-
! Elevation<ref name=EPA/>
| {{convert|571|ft|m|abbr=on|order=flip}}
| {{convert|577|ft|m|abbr=on|order=flip}}
| {{convert|577|ft|m|abbr=on|order=flip}}
| {{convert|246|ft|m|abbr=on|order=flip}}
| {{convert|600.0|ft|m|abbr=on|order=flip}}
|-
! Average depth<ref name="Grady" />
| {{convert|62|ft|m|abbr=on|order=flip}}
| {{convert|195|ft|m|abbr=on|order=flip}}
| {{convert|279|ft|m|abbr=on|order=flip}}
| {{convert|283|ft|m|abbr=on|order=flip}}
| {{convert|483|ft|m|abbr=on|order=flip}}
|-
! Maximum depth<ref name="dep">{{cite web |title = Great Lakes Map |url = http://www.michigan.gov/deq/0,1607,7-135-3313_3677-15926--,00.html |publisher = Michigan Department of Environmental Quality |access-date = November 27, 2011 |archive-url = https://web.archive.org/web/20111114034432/http://www.michigan.gov/deq/0,1607,7-135-3313_3677-15926--,00.html |archive-date = November 14, 2011 |url-status = dead }}</ref>
| {{convert|210|ft|m|abbr=on|order=flip}}
| {{convert|748|ft|m|abbr=on|order=flip}}
| {{convert|925|ft|m|abbr=on|order=flip}}
| {{convert|804|ft|m|abbr=on|order=flip}}
| {{convert|1333|ft|m|abbr=on|order=flip}}
|-
! Major settlements<ref>See [[List of cities on the Great Lakes]] for a complete list.</ref>
| [[Buffalo, New York|Buffalo, NY]]<br />[[Erie, Pennsylvania|Erie, PA]]<br />[[Cleveland|Cleveland, OH]]<br />[[Detroit|Detroit, MI]]<br/>[[Lorain, Ohio|Lorain, OH]]<br />[[Toledo, Ohio|Toledo, OH]]<br />[[Sandusky, Ohio|Sandusky, OH]]
| [[Alpena, Michigan|Alpena, MI]]<br />[[Bay City, Michigan|Bay City, MI]]<br />[[Collingwood, Ontario|Collingwood, ON]]<br />[[Owen Sound|Owen Sound, ON]]<br />[[Port Huron, Michigan|Port Huron, MI]]<br />[[Sarnia|Sarnia, ON]]
| [[Chicago|Chicago, IL]]<br />[[Waukegan|Waukegan, IL]]<br />[[Gary, Indiana|Gary, IN]]<br />[[Green Bay, Wisconsin|Green Bay, WI]]<br />[[Sheboygan, Wisconsin|Sheboygan, WI]]<br />[[Milwaukee|Milwaukee, WI]]<br />[[Kenosha, Wisconsin|Kenosha, WI]]<br />[[Racine, Wisconsin|Racine, WI]]<br />[[Muskegon, Michigan|Muskegon, MI]]<br />[[Traverse City, Michigan|Traverse City, MI]]
| [[Hamilton, Ontario|Hamilton, ON]]<br />[[Kingston, Ontario|Kingston, ON]]<br />[[Mississauga|Mississauga, ON]]<br />[[Oshawa|Oshawa, ON]]<br />[[Rochester, New York|Rochester, NY]]<br />[[Toronto|Toronto, ON]]
| [[Duluth, Minnesota|Duluth, MN]]<br />[[Marquette, Michigan|Marquette, MI]]<br />[[Sault Ste. Marie, Michigan|Sault Ste. Marie, MI]]<br />[[Sault Ste. Marie, Ontario|Sault Ste. Marie, ON]]<br />[[Superior, Wisconsin|Superior, WI]]<br />[[Thunder Bay|Thunder Bay, ON]]
|}As the surfaces of Lakes Superior, Huron, Michigan, and Erie are all approximately the same elevation above sea level, while Lake Ontario is significantly lower, and because the [[Niagara Escarpment]] precludes all natural navigation, the four upper lakes are commonly called the "upper great lakes". This designation is not universal. Those living on the shore of Lake Superior often refer to all the other lakes as "the lower lakes", because they are farther south. Sailors of [[Bulk carrier|bulk freighters]] transferring cargoes from Lake Superior and northern Lake Michigan and Lake Huron to ports on Lake Erie or Ontario commonly refer to the latter as the lower lakes and Lakes Michigan, Huron, and Superior as the upper lakes. This corresponds to thinking of lakes Erie and Ontario as "down south" and the others as "up north". Vessels sailing north on Lake Michigan are considered "upbound" even though they are sailing toward its effluent current.<ref name="Bowlus2010">{{cite book |first = W. Bruce |last = Bowlus |title = Iron Ore Transport on the Great Lakes: The Development of a Delivery System to Feed American Industry |url = https://books.google.com/books?id=nyGjHG1PaUEC&pg=PA215 |year = 2010 |publisher = McFarland |isbn = 978-0-7864-8655-7 |page = 215 }}</ref>{{clear}}

[[File:Great Lakes.svg|upright=1.8|thumb|left|System profile of the Great Lakes]]
{{clear}}

===Primary connecting waterways===
[[File:2009-09-18 3060x2040 chicago skyline.jpg|thumb|right|Chicago on Lake Michigan is in the western part of the lakes megalopolis and the site of the waterway linking the lakes to the Mississippi River valley]]

* The [[Chicago River]] and [[Calumet River]] systems connect the Great Lakes Basin to the [[Mississippi River]] System through human-made alterations and canals.
* The [[St. Marys River (Michigan–Ontario)|St. Marys River]], including the [[Soo Locks]], connects Lake Superior to Lake Huron, via the [[North Channel (Ontario)|North Channel]].
* The [[Straits of Mackinac]] connect Lake Michigan to Lake Huron (the two are hydrologically one lake).
* The [[St. Clair River]] connects Lake Huron to [[Lake St. Clair]].
* The [[Detroit River]] connects Lake St. Clair to Lake Erie.
* The [[Niagara River]], including [[Niagara Falls]], connects Lake Erie to Lake Ontario.
* The [[Welland Canal]], bypassing the Niagara River, connects Lake Erie to Lake Ontario.
* The [[Saint Lawrence River]] and the [[Saint Lawrence Seaway]] connect Lake Ontario to the [[Gulf of Saint Lawrence]], which connects to the [[Atlantic Ocean]].

===Lake Michigan–Huron===
{{main|Lake Michigan–Huron}}
[[File:ISS067-E-14016 Lake Michigan–Huron.jpg|thumb|Lake Michigan–Huron with north oriented to the right; taken on April 14, 2022, during [[Expedition 67]] of the International Space Station. {{nowrap|Green Bay}} is at the upper right and Saginaw Bay is on the left.]]
Lakes Huron and Michigan are sometimes considered a single lake, called Lake Michigan–Huron, because they are one hydrological body of water connected by the Straits of Mackinac.<ref>{{cite web |url = http://www.infoplease.com/ipa/A0001804.html |title = Michigan and Huron: One Lake or Two? |publisher = Pearson Education |website = Information Please Database |year = 2007 }}</ref> The straits are {{convert|5|mi|km|0|spell=in}} wide<ref name="Grady" /> and {{convert|120|ft|m}} deep; the water levels rise and fall together,<ref name=nyt>{{cite book |editor-first = John W. |editor-last = Wright |year = 2006 |title = The New York Times Almanac |url = https://archive.org/details/newyorktimes200600wrig |url-access = registration |edition = 2007 |publisher = Penguin Books |location = New York |isbn = 978-0-14-303820-7 |page = [https://archive.org/details/newyorktimes200600wrig/page/64 64] }}</ref> and the flow between Michigan and Huron frequently reverses direction.

===Large bays and related significant bodies of water===
* [[Lake Nipigon]], connected to Lake Superior by the [[Nipigon River]], is surrounded by [[layered intrusion|sill-like formations]] of [[mafic]] and [[ultramafic rock|ultramafic]] [[igneous rock]] hundreds of meters high. The lake lies in the [[Nipigon Embayment]], a [[Aulacogen|failed arm]] of the [[triple junction]] (centered beneath Lake Superior) in the [[Midcontinent Rift System]] event, estimated at 1.1 billion years ago.
* [[Thunder Bay (Ontario)|Thunder Bay]] is a large bay on the north shore of Lake Superior bordered to the east by the [[Sibley Peninsula]] in northern Ontario.
* [[Chequamegon Bay]] is an inlet of Lake Superior south of the [[Apostle Islands]] and the [[Bayfield Peninsula]] in northern Wisconsin.
* [[Keweenaw Bay]] is an arm of Lake Superior southeast of the [[Keweenaw Peninsula]].
* [[Whitefish Bay]] is a large bay on the eastern end of Lake Superior which leads to the outflow of the lake into the [[St. Marys River (Michigan–Ontario)|St. Marys River]].
* [[Lake Winnebago]], connected to Green Bay by the [[Fox River (Green Bay tributary)|Fox River]], serves as part of the [[Fox–Wisconsin Waterway]] and is part of a larger system of lakes in Wisconsin known as the [[Winnebago Pool]].
* [[Green Bay (Lake Michigan)|Green Bay]] is an arm of Lake Michigan along the south coast of the [[Upper Peninsula of Michigan]] and the east coast of Wisconsin. It is separated from the rest of the lake by the [[Door Peninsula]] in Wisconsin, the [[Garden Peninsula]] in Michigan, and the chain of islands between them, all of which were formed by the [[Niagara Escarpment]]. The north end of Green Bay consists of [[Big Bay de Noc]] and [[Little Bay de Noc]].
* [[Grand Traverse Bay]] is an arm of Lake Michigan on Michigan's west coast and is one of the largest natural harbors in the Great Lakes. The bay is divided into east and west arms by the [[Old Mission Peninsula]].<ref>{{cite web |url = http://www.peninsulatownship.com |title = Home |publisher = Peninsula Township |access-date = December 7, 2016 }}</ref> The bay has one major island, [[Power Island]]. Its name is derived from [[Jacques Marquette|Jacques Marquette's]] crossing of the bay from [[Norwood, Michigan|Norwood]] to [[Northport, Michigan|Northport]] which he called ''La Grande Traversee''.{{citation needed|date=May 2016}}
* [[Georgian Bay]] is an arm of Lake Huron, extending northeast from the lake entirely within Ontario. The bay, along with its narrow westerly extensions of the [[North Channel (Ontario)|North Channel]] and [[Mississagi Strait]], is separated from the rest of the lake by the [[Bruce Peninsula]], [[Manitoulin Island]], and [[Cockburn Island (Ontario)|Cockburn Island]], all of which were formed by the Niagara Escarpment.
* [[Lake Nipissing]], connected to Georgian Bay by the [[French River (Ontario)|French River]], contains two [[volcanic pipe]]s, which are the [[Manitou Islands (Lake Nipissing)|Manitou Islands]] and [[Callander Bay]].<ref>{{cite web |url = http://home.cogeco.ca/~nananne/backgroundgeology/070211-BackgroundGeology-w.html |title = Background Geology of the North Bay area |archive-url = https://web.archive.org/web/20100724012748/http://home.cogeco.ca/~nananne/backgroundgeology/070211-BackgroundGeology-w.html |archive-date = July 24, 2010 |access-date = September 24, 2007 }}{{self-published inline|certain=yes|date=March 2024}}</ref> These pipes were formed by a violent, [[supersonic eruption]] of deep origin. The lake lies in the [[Ottawa-Bonnechere Graben]], a [[Mesozoic]] [[rift valley]] that formed 175&nbsp;million years ago.
* [[Lake Simcoe]], connected to Georgian Bay by the [[Severn River (central Ontario)|Severn River]], serves as part of the [[Trent–Severn Waterway]], a canal route traversing [[Southern Ontario]] between Lakes Ontario and Huron.
* [[Thunder Bay (Michigan)|Thunder Bay]] is a bay on the west side of Lake Huron in Michigan.
* [[Saginaw Bay]], an extension of Lake Huron into the [[Lower Peninsula of Michigan]], fed by the [[Saginaw River|Saginaw]] and other rivers, has the largest contiguous freshwater [[wetland]] in the United States.<ref>{{Cite web |url = https://www.epa.gov/greatlakes |title = The Great Lakes |id = REG 05 |date = August 20, 2015 |publisher = Environmental Protection Agency }}</ref>
* [[Lake St. Clair]], connected with Lake Huron to its north by the [[St. Clair River]] and with Lake Erie to its south by the [[Detroit River]]. Although it is 17 times smaller in area than Lake Ontario and only rarely included in the listings of the Great Lakes,<ref name=LakeStClair>{{cite web |url = http://www.great-lakes.net/lakes/stclairReport/summary_00.pdf |title = Lake St. Clair summary report |archive-url = https://web.archive.org/web/20160416124842/http://www.great-lakes.net/lakes/stclairReport/summary_00.pdf |archive-date = April 16, 2016 |website = Great Lakes.net |access-date = December 2, 2007 }}</ref><ref name="U.S.Army">{{cite web |url = http://www.lre.usace.army.mil/_kd/Items/actions.cfm?action=Show&item_id=4310&destination=ShowItem |title = Chapter 1:Introduction to Lake St. Clair and the St. Clair River |access-date = June 8, 2008 |publisher = U.S. government U.S. Army |date = June 2004 |archive-url = https://web.archive.org/web/20090110202934/http://www.lre.usace.army.mil/_kd/Items/actions.cfm?action=Show&item_id=4310&destination=ShowItem |archive-date = January 10, 2009 }}</ref> proposals for its official recognition as a Great Lake are occasionally made, which would affect its inclusion in scientific research projects designated as related to "The Great Lakes".<ref>{{cite news |url = https://www.latimes.com/archives/la-xpm-2002-oct-20-na-stclair20-story.html |title = Movement Would Thrust Greatness on Lake St. Clair |newspaper = [[Los Angeles Times]] |date = October 20, 2002 }}</ref>
* [[Sandusky Bay]] is a bay on Lake Erie in northern Ohio.
* [[Long Point, Ontario|Long Point Bay]] is a bay on the north shore of Lake Erie in Ontario.
* [[Hamilton Harbour]] is a harbor on the western tip of Lake Ontario.
* The [[Bay of Quinte]] is a long and narrow bay on the north shore of Lake Ontario.

===Islands===
[[File:Put-in-Bay Airport.jpg|thumb|[[South Bass Island]] in Lake Erie]]
Dispersed throughout the Great Lakes are approximately [[List of islands of the Great Lakes|35,000 islands]].<ref name="Bennett1999as"/> The largest among them is [[Manitoulin Island]] in Lake Huron, the largest island in any inland body of water in the world.<ref name="Dunn1996bv">{{cite book |last = Dunn |first = Gary A |title = Insects of the Great Lakes Region |url = https://books.google.com/books?id=HWHXdlPF-7cC&pg=PA3 |year = 1996 |publisher = [[University of Michigan Press]] |isbn = 978-0-472-06515-8 |page = 3 }}</ref> The second-largest island is [[Isle Royale]] in Lake Superior.<ref name="Huber(U.S.)1975">{{cite book |last1 = Huber |first1 = Norman King |author2 = United States Geological Survey |author3 = United States National Park Service |title = The geologic story of Isle Royale National Park |url = https://books.google.com/books?id=Te8sAQAAMAAJ&pg=PA41 |year = 1975 |publisher = Government Printing Office |page = 41 |isbn = 9780932212313 }}</ref> Both of these islands are large enough to contain multiple lakes themselves—for instance, Manitoulin Island's [[Lake Manitou]] is the world's largest lake on a freshwater island.<ref name="Manivanan2008">{{cite book |last = Manivanan |first = R. |title = Water Quality Modeling: Rivers, Streams, and Estuaries |url = https://books.google.com/books?id=KneEuR09lsQC&pg=PA114 |year = 2008 |publisher = New India Publishing |isbn = 978-81-89422-93-6 |page = 114 }}</ref> Some of these lakes even have their own islands, like [[Treasure Island (Ontario)|Treasure Island]] in [[Lake Mindemoya]] in Manitoulin Island.

===Peninsulas===
[[File:Skyline of Toronto viewed from Harbour.jpg|thumb|right|[[Toronto]] on Lake Ontario is in the eastern section of the [[Great Lakes Megalopolis]]]]
The Great Lakes have several peninsulas between them, most prominently the [[Upper Peninsula of Michigan|Upper Peninsula]], the [[Lower Peninsula of Michigan|Lower Peninsula]], and the [[Ontario Peninsula]]. Population centers on these peninsulas include [[Grand Rapids, Michigan|Grand Rapids]], [[Flint, Michigan|Flint]], and [[Detroit, Michigan|Detroit]] in Michigan along with [[London, Ontario|London]], [[Hamilton, Ontario|Hamilton]], [[Brantford, Ontario|Brantford]], and [[Toronto, Ontario|Toronto]] in Ontario. Other significant peninsulas in the Great Lakes include the [[Sibley Peninsula|Sibley]], [[Bayfield Peninsula|Bayfield]], [[Keweenaw Peninsula|Keweenaw]], [[Door Peninsula|Door]], [[Garden Peninsula|Garden]], [[Leelanau Peninsula|Leelanau]], [[The Thumb|Thumb]], [[Bruce Peninsula|Bruce]], and [[Niagara Peninsula|Niagara]] peninsulas.

===Shipping connection to the ocean===
Although the Saint Lawrence Seaway and Great Lakes Waterway make the Great Lakes accessible to ocean-going vessels,<ref name="McCalla1994">{{cite book |first = Robert |last = McCalla |title = Water Transportation in Canada |url = https://archive.org/details/watertransportat0000mcca |url-access = registration |date = January 1, 1994 |publisher = Formac Publishing Company |isbn = 978-0-88780-247-8 |pages = [https://archive.org/details/watertransportat0000mcca/page/159 159]–162 }}</ref> shifts in shipping to wider ocean-going [[container ship]]s—which do not fit through the [[Lock (water navigation)|locks]] on these routes—have limited container shipping on the lakes. Most Great Lakes trade is of bulk material, and bulk freighters of [[Seawaymax]]-size or less can move throughout the entire lakes and out to the Atlantic.<ref name="Coastal Sediments '07">{{cite book |title = Coastal Sediments '07 |url = https://books.google.com/books?id=iMt2BQ0R628C&pg=PA2215 |access-date = April 16, 2013 |year = 2007 |publisher = ASCE Publications |isbn = 978-0-7844-7194-4 |page = 2215 }}</ref> Larger ships are confined to working within the lakes. Only barges can access the [[Illinois Waterway]] system providing access to the [[Gulf of Mexico]] via the Mississippi River. Despite their vast size, large sections of the Great Lakes freeze over in winter, interrupting most shipping from January to March. Some [[icebreaker]]s ply the lakes, keeping the shipping lanes open through other periods of ice on the lakes.

The Great Lakes are connected by the [[Chicago Sanitary and Ship Canal]] to the Gulf of Mexico via the [[Illinois River]] (from the [[Chicago River]]) and the Mississippi River. An alternate track is via the Illinois River (from Chicago), to the Mississippi, up the Ohio, and then through the [[Tennessee–Tombigbee Waterway]] (a combination of a series of rivers and lakes and canals), to [[Mobile Bay]] and the Gulf of Mexico. Commercial [[Tugboat|tug]]-and-[[barge]] traffic on these waterways is heavy.<ref name="Census1908">{{cite book |author = United States Bureau of the Census |title = Transportation by water. 1906 |url = https://archive.org/details/transportationb00censgoog |year = 1908 |publisher = Government Printing Office |page = [https://archive.org/details/transportationb00censgoog/page/n252 220] }}</ref>

Pleasure boats can enter or exit the Great Lakes by way of the [[Erie Canal]] and [[Hudson River]] in New York. The Erie Canal connects to the Great Lakes at the east end of Lake Erie (at [[Buffalo, New York]]) and at the south side of Lake Ontario (at [[Oswego, New York]]).

===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>

===Ice cover===
The annual ice coverage on the Great Lakes varies greatly from year to year due to weather patterns and long-term climate trends. Ice typically begins forming in December and reaches its peak in February or early March.<ref name="eonasa">{{cite web |title=New Lows for Great Lakes Ice Cover |url=https://earthobservatory.nasa.gov/images/152502/new-lows-for-great-lakes-ice-cover |website=Earth Observatory |publisher=NASA |access-date=5 April 2025 |language=en |date=29 February 2024}}</ref> The extent of ice cover can vary from as little as 10% to over 90% depending on winter severity. For example, during the particularly cold winter of 2013–2014, ice coverage peaked at over 92% across the five lakes, while in milder years like 2023–2024, coverage remained below 20%.<ref name="noaaice">{{cite web |title=Great Lakes Ice Cover |url=https://www.glerl.noaa.gov/data/ice/ |website=Great Lakes Environmental Research Laboratory |publisher=National Oceanic and Atmospheric Administration |access-date=5 April 2025 |language=EN-US}}</ref> Long-term data from the [[National Oceanic and Atmospheric Administration]]'s [[Great Lakes Environmental Research Laboratory]] (NOAA GLERL) indicate a general decline in maximum ice cover over the past few decades, aligning with broader patterns of warming in the region.<ref name="eonasa"/><ref>{{cite web |title=Great Lakes Ice |url=https://www.climatecentral.org/climate-matters/great-lakes-ice-2024 |date=7 February 2024 |website=Climate Central |access-date=5 April 2025 |language=en}}</ref>