Volume 208: 2020 Annual Summary

Background

The U.S. Army Corps of Engineers (USACE) 

monitors and forecasts the water levels of each of 

the Great Lakes. This report is primarily focused 

on summarizing the hydrologic conditions of the 

Great Lakes basin in 2020.

Official water levels are based on monthly lakewide means, and the period of record used for each 

of the lakes includes the years 1918 to 2019. These 

data have been coordinated between the United 

States and Canada. 

The elevations used are referenced to the 

International Great Lakes Datum of 1985. The 

water level of each lake is averaged from a 

network of individual gages around each lake. 

Also of note is that Lake Michigan and Lake 

Huron are hydraulically treated as one lake due to 

their connection at the Straits of Mackinac.

The Great Lakes are very large and behave 

differently from smaller, inland lakes. In general, 

Great Lakes water levels do not rise and fall with 

individual storms. Significant water level 

fluctuations require multiple months, seasons, or 

years of wet or dry conditions.

Seasonal changes in weather patterns typically 

cause an annual pattern of rising and falling of 

Great Lakes water levels. Each of the Great Lakes 

exhibits a seasonal rise in the spring primarily 

caused by an increase in liquid precipitation, 

increased runoff due to melting of accumulated 

snow, and low evaporation rates. The typical 

seasonal decline of the water levels in the fall and 

winter is primarily caused by an increase in 

evaporation, a decrease in precipitation, and the 

accumulation of snowpack on the land area.

The Net Basin Supply (NBS) is an important 

quantity for understanding the amount of water 

which arrives to the lake. USACE uses the 

residual method to compute NBS, shown below in 

the summarizing equations: 

Residual Method Net Basin Supply:

NBS = WL – I – D + O

WL: Water Level Change

I: Connecting Channel Inflow

O: Connecting Channel Outflow

D: Diversion into(+) or out(-) of lake

Altogether, NBS represents the combined effects 

of precipitation over the lake, runoff to the lake, 

and evaporation off of the lake. NBS is the main 

driver of water levels and is also discussed in more 

detail in the following sections for each lake. All 

2019 and 2020 NBS data discussed in this 

publication is preliminary.

Record-High Water Levels in 2020

All the Great Lakes, besides Lake Ontario,

remained significantly above average in 2020.

Lakes Superior, Michigan-Huron, St. Clair and 

Erie have been above their monthly average levels 

since at least November 2015 and continued 

through 2020. Lakes Superior, Michigan-Huron, 

St. Clair, and Erie all matched or set record high

monthly mean levels in 2020. Lake MichiganHuron set new monthly mean records January 

Great Lakes

Update
Vol. 208 Great Lakes Update February 2021 

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through August. Table 1 below summarizes the 

months in which record high water levels were met 

or surpassed in 2020. 

Table 1. Year record high level set on each 

Great Lake dating back to 1918. 

*Previous record set in 2019.

Record high outflows occurred from January 

through November in the Great Lakes basin. Table

2 shows the outflow records for each connecting 

channel. The St. Clair River, Detroit River, and 

Niagara River had more than six months each of 

record high outflows. All 2020 connecting 

channel data discussed in this article is provisional.

Table 2. Record high levels experienced on 

connecting channels.

Connecting 

Channel Time Period

St. Clair River January through September

Detroit River January through October

Niagara River January through April

St. Lawrence River January through March

Lake Superior

Figure 1 shows the 2020 water levels of Lake 

Superior compared with the 2019 levels and the 

monthly long-term average (LTA) levels. A 

similar figure is shown for each lake in the 

following sections. Each lake’s data has been 

plotted relative to chart datum (a.k.a. low water 

datum). Chart datum for Lake Superior is 601.1 

feet. The dark line in Figure 1 represents the daily 

2020 water levels and the solid gray line shows the 

2019 levels. The LTA levels for each month are 

shown as circles and maximums and minimums 

are represented as yellow and blue dashes, 

respectively. Figure 2 shows monthly residual 

NBS, and the NBS is shown as a difference (in 

inches) from the monthly LTA NBS. The lake’s 

annual NBS, which is the sum of the monthly NBS 

for all twelve months, dropped below its average 

for the first time in the last eight years. The lake’s 

2020 annual NBS compared to recent annual NBS 

is provided in Table 3. 

Figure 1. Lake Superior Water Levels

Figure 2. Lake Superior Residual Net Basin 

Supply deviation from Long-Term Average

LAKE JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

SUP 2020 2020 1986 1986 2019 2019 2019 2019 2019 1985 1985 1985

M-H 2020 2020 2020 2020 2020 2020 2020 2020 1986 1986 1986 1986

STC 2020 1986 2020 2020 2020* 2020* 2019 2020* 2020* 1986 1986 1986

ERI 1987 2020 2020 2020 2020* 2019 2019 2019 2019 1986 1986 1986

ONT 1946 1952 1952 1973 2017 2019 2019 1947 1947 1945 1945 1945
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Table 3. Lake Superior’s Annual NBS from 

2013-2020 compared to its Average Annual 

NBS

Above average NBS and above normal 

temperatures likely resulted in enhanced runoff 

and reduced evaporation in January. Lake Superior 

started 2020 with a January monthly mean level of 

602.72 feet, which surpassed its record-high 

January level previously set in 1986 by nearly half 

an inch. This record-high level was 4 inches above 

last January’s level and 15 inches above the LTA

January level. Lake Superior exceeded its monthly 

mean records by less than an inch in January and 

February before dipping below record high 

monthly means from March through December. 

In February, Lake Superior received about 40% of 

its average precipitation; coupled with above 

average evaporation resulted in a well below 

average NBS for the month. NBS was below 

average in 4 of the next 6 months. According to 

preliminary data, runoff was below average the 

final 9 months of 2020, while evaporation was 

above average in all but one month between 

February and October. In addition, precipitation in 

the Lake Superior basin in 2020 was around 80% 

of its annual average. Lake Superior reached its 

peak monthly average level of 603.05 feet in 

August. The lake was higher than its LTA by 9 to 

15 inches throughout 2020. Lake Superior rose 

slightly more than 9 inches compared to its 2019 

rise of 12 inches. By the end of 2020, Lake 

Superior had been above its monthly LTA levels 

every month since April 2014; an 81-month 

period. 

Lake Michigan-Huron

Water levels for Lake Michigan-Huron in 2020 are 

shown in Figure 3. The lake’s monthly mean level 

in January was 581.56 feet; 3 inches higher than its 

previous record high from 1987, 18 inches above 

January 2019 level and 38 inches above its LTA.

Winter 2019 - 2020 saw lower than average 

seasonal decline of 6 inches when the average is 

around 12 inches. Near-record high NBS in 

January and a lower seasonal decline likely

contributed to the lake breaking its monthly mean 

records from January through August. January 

through June monthly means broke the prior 

record high by 3 to 6 inches. 

Figure 3. Lake Michigan-Huron Water Levels

Water levels on Lake Michigan-Huron have been 

higher than average every month since October 

2014, a streak of 75 consecutive months. Lake 

Michigan-Huron’s seasonal rise of 9 inches in 

2020 was significantly lower than its rise of 22 

inches in 2019 and its historical average seasonal 

rise of 12 inches. The lake peaked in July at a 

monthly mean level of 582.19 feet. 

Figure 4 shows monthly residual net basin supply 

relative to its monthly LTA NBS. Moreover, NBS 

was above average in 7 of the last 10 months of the 

year. Precipitation was above average in 5 of those 

7 months. Table 4 shows a summary of the annual 

NBS over the past 7 years. Annual NBS to Lake 

Michigan-Huron in 2020 ranked 12th highest in the 
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period of record starting in 1900 and January 

experienced the 3rd highest NBS for the month. In 

addition, October 2019 to March 2020 was a 

record high 6-month period of NBS. 

Figure 4. Lake Michigan-Huron Residual Net 

Basin Supply, difference from Long-Term 

Average

Table 4. Lake Michigan-Huron’s Annual NBS 

from 2013-2020 compared to its Average 

Annual NBS

Lake St. Clair 

Lake St. Clair met or exceeded monthly mean 

records in January, March through June, August, 

and September. Figure 5 shows the water levels of 

Lake St. Clair in 2020 compared to 2019 and the 

LTA levels. Lake St. Clair started the year 37 

inches above LTA and 15 inches above January 

2019 levels. In addition, the lake has been above 

its monthly LTA every month since March 2015. 

Lake St. Clair matched its January record high 

monthly mean level originally set in 1986 and was 

below its February monthly mean record by less 

than half an inch while still being 15 inches above 

its February 2019 water level. Above average 

precipitation in January and above average NBS in 

February and March resulted in levels being 8 to 

15 inches higher from January through April than 

2019 levels. Lake St. Clair rose a total of 14 inches 

in 2020, far below its 2019 rise of 25 inches. The 

lake’s decline from its July peak to December was 

16 inches, slightly higher than its average July-toDecember decline of 11 inches, resulting in Lake 

St. Clair being 7 to 9 inches below record highs 

during the final three months of the year. 

 NBS was above average the first and last 3 months

of 2020. The lake’s monthly NBS is summarized 

in Figure 6. 

Figure 5. Lake St. Clair Water Levels

Figure 6. Lake St. Clair Net Basin Supplies

Lake Erie

Lake Erie experienced record-breaking high-water

levels in 2020, as displayed in Figure 7. Lake 

levels have been above their monthly LTA since 
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June 2015, a period of 67 consecutive months. 

Lake Erie began its seasonal rise in December 

2019 while it historically starts its seasonal rise in 

February, likely contributing to its record-high 

levels February through May 2020. The lake’s 

January 2020 monthly mean level was about 7 

inches above its 2019 January level, 31 inches 

above its LTA, and just 2 inches below its January 

record-high monthly level. Lake Erie rose 17 

inches in 2020, exceeding its historical average 

climb of 14 inches. Monthly mean levels remained 

7 to 12 inches above the 2019 levels and 31 to 35 

inches above the LTA over the first four months of 

2020. However, over the final seven months of 

2020, Lake Erie monthly mean levels ranged from 

1 to 4 inches below its corresponding 2019 

monthly levels.

Significantly above average NBS in January was a 

result of increased snowmelt and a higher fraction 

of precipitation falling as rain - both attributable to 

above average temperatures in the basin. The 

lake’s monthly NBS in 2020 and 2019 are shown 

as a difference from average in Figure 8. 

Precipitation was below average 6 of the last 9 

months of 2020, annual precipitation in 2020 was 

89% of average, and there were no months of 

above average runoff after January. These factors 

likely contributed to Lake Erie receiving merely 

63% of the average annual NBS in 2020. Lake 

Erie’s levels remained well above average 

throughout 2020. Lake Erie declined 18 inches 

from its peak in June to December.

Figure 7. Lake Erie Water Levels

Figure 8. Lake Erie Residual Net Basin 

Supply, deviation from Long-Term Average

Lake Ontario

Figure 9 shows Lake Ontario water levels relative 

to the chart datum of 243.3 feet. In 2020 Lake 

Ontario began 9 inches above last January’s level, 

19 inches above LTA, and 4 inches below its 

record high January level. Lake Ontario 

experienced its 4th highest January NBS since 

1900. Unlike the other Great Lakes, which have 

been above average in every month since at least 

late 2015, Lake Ontario’s current streak of above 

average water levels began in November 2018. 

The lake’s seasonal rise in 2020 was 14 inches, 

which was substantially less than the seasonal rise 

of 51 inches in 2019, and its average seasonal rise 

of 21 inches. Lake Ontario’s monthly NBS, shown 

in Figure 13, was below average for eight 

consecutive months from April through 

November. Lake Ontario peaked in May at 247.24 

feet, 13 inches below its May 2019 level, 13 inches 
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above LTA level, and 17 inches below its record 

high level. 

The lake’s 30-inch seasonal decline in 2020

occurred from May to November and was above 

the lake’s average June to December decline of 21

inches. This decline brought Lake Ontario down to 

15 inches below its 2019 monthly mean level, 4 

inches above LTA, and 23 inches below the record 

high in December. Record high monthly Lake 

Ontario connecting channel inflows from the 

Niagara River in the beginning of the year may 

have contributed to the lake’s sustained above 

average water levels as well. 

Figure 9. Lake Ontario Water Levels

Figure 10. Lake Ontario Residual Net Basin 

Supply, deviation from Long-Term Average

Emergency Management Rises to the Occasion

The U.S. Army Corps of Engineers (USACE) 

Emergency Management is authorized by Public 

Law 84-99 to support local, county, and state 

efforts during flood emergencies. USACE support 

comes in two forms, Technical Assistance and 

Direct Assistance. Technical Assistance allows 

USACE to provide data, recommendations and 

solutions to the community’s flooding concerns. 

Additionally, under Technical Assistance, USACE 

can deploy a skilled flood fight team during a flood 

event in order to bring expertise into a community, 

and train local communities how to properly fill 

and place sandbags and other temporary flood 

protection measures. Under Direct Assistance, 

USACE can provide materials and equipment to 

communities during a flooding event. These 

materials include sandbags, plastic sheeting, and 

HESCO barriers. All materials provided must be 

returned if not used or reimbursed back to USACE, 

unless a Presidential Disaster is declared. 

Additionally, flood fight supplies provided under 

Direct Assistance are solely for the protection of 

critical public infrastructure. USACE cannot 

directly assist individual homeowners or 

commercial interests.

2020-2021 Great Lakes High Water 

Due to the rising water level on the Great Lakes, 

USACE Detroit District activated their Emergency 

Operations Center (EOC) in early May 2019. 

Since the start of this event, Emergency 

Management has provided Technical Assistance to 

one county in Wisconsin, one county in 

Minnesota, thirteen counties in Michigan, and one 

tribe in Michigan. Typical Technical Assistance 

for coastal flooding concerns has included 

reviewing areas of concern and providing flood 

fighting recommendations and educating/training 

in proper sandbag filling and placement. In 

addition to Technical Assistance, the Detroit 

District has provided Direct Assistance to the City 

of Detroit in the form of sandbags and HESCO 

barriers, as well as the City of South Haven in the 

form of HESCO barriers. Finally, the Detroit 

District has provided over 350,000 sandbags to 

local communities as part of a onetime inventory 

drawdown initiative. The Detroit District EOC 

still remains activated.
Vol. 208 Great Lakes Update February 2021 

Page 7

Preparedness is a key principle in Emergency 

Management, and USACE Detroit District 

Emergency Management has been engaged with 

many communities in Michigan, Wisconsin, and 

Minnesota to provide outreach regarding the 

ongoing threat from the Great Lakes high water 

levels. These engagements range from one-on-one 

meetings with local/county government agencies, 

to virtual education initiatives, to public

meetings/presentations on Great Lakes water 

levels, USACE Emergency Management 

authorities, and the Detroit District response to the 

Great Lake high water level event. 

Case Study: Direct Assistance in Michigan 

Communities

Figure 15: HESCO placement in South Haven, 

MI, April 2020. 

Figure 16: Sandbagging and HESCO 

placement in Jefferson-Chalmers community, 

Detroit, MI, May 2020 

During the spring of 2020, the Cities of Detroit and 

South Haven in Michigan experienced substantial 

flooding along the shore of Lakes St. Clair and 

Michigan, respectively. Flooding caused damage 

to numerous homes, streets to become impassible, 

evacuation routes to be blocked, and threatened 

critical public infrastructure. At the request of key 

stakeholders, the USACE Detroit District Flood 

Fight Team (FFT) was deployed to support the 

Jefferson-Chalmers community in Detroit. 

Similarly, the City of South Haven partnered with

USACE in order to protect the city’s Wastewater 

Treatment Facility and Water Filtration Plant. 

Much like in 2019, these were community led 

events, assisted by USACE and other partners. 

The Flood Fight Team, along with a USACEprovided HESCO representative, assisted 

stakeholders in the proper placement, construction, 

and filling of the HESCO barriers and sandbags. 

Who Can You Contact? 

If you need assistance in your community, please 

contact your local or county emergency 

management agency. USACE support is 

supplemental to local efforts and it is important 

that the county and state are aware of the need in 

their area of responsibility. If you have any 

questions for USACE Detroit District, please 
Vol. 208 Great Lakes Update February 2021

Page 8

contact Emergency Management at CELREEOC@usace.army.mil or visit our dedicated Great 

Lakes High Water webpage at 

https://www.lre.usace.army.mil/About/GreatLakes-High-Water/

More Information

Update articles are included periodically in the 

Monthly Bulletins highlighting topics and 

explanations relevant to Great Lakes water levels. 

Nearly all past Update Articles dating back to 1985 

can be accessed here:

https://www.lre.usace.army.mil/Missions/Great-LakesInformation/News-and-Information/Great-Lakes-UpdateArticles/

The Monthly Bulletin is sent by postal mail. To be 

added to the postal mailing list, please send an 

email to hhpm@usace.army.mil or call 1-888-694-

8313 and select option 1. Alternatively, the 

Monthly Bulletin can be viewed on our website. 

The home page is: http://www.lre.usace.army.mil. 

In addition to the Monthly Bulletin, the Detroit 

District issues the Weekly Great Lakes Water Level 

Update and the Weekly Great Lakes Connecting 

Channels Water Levels and Depths. Both products 

are updated at the end of each week. All forecast 

products are located here:

https://www.lre.usace.army.mil/Missions/Great-LakesInformation/Great-Lakes-Water-Levels/Water-LevelForecast/

Additionally, a product called Great Lakes Water 

Level Future Scenarios illustrates outcomes that 

would occur under historical weather and water 

supply conditions, with scenarios chosen based on 

similarities to recent conditions. This product is 

updated every three months and is located here:

https://www.lre.usace.army.mil/Missions/Great-LakesInformation/Great-Lakes-Water-Level-Future-Scenarios/

The Detroit District also has a Facebook page 

which can be found here:

https://www.facebook.com/USACEDetroitDistrict/

Please email questions and comments to 

hhpm@usace.army.mil. To contact the District by 

phone call toll free 1-888-694-8313 and select 

option 1. The Detroit District’s mailing address is:

Department of the Army

Detroit District Corps of Engineers

ATTN: CELRE-EHW

477 Michigan Avenue

Detroit, MI 48226