Volume 199: 2017 Annual Summary

Background

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

tracks 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 2017.

Over the last year, all of the lakes have experienced 

above average water levels. The 2017 water levels 

surpassed those of 2016 by spring and remained at 

higher levels for the remainder of the year. 

Generally, water levels since the spring of 2017

have been near or above levels of the last high 

water period during the late 1990s.

Official water levels are based on monthly lakewide averages from a network of individual gages 

around each lake. These data have been 

coordinated between the United States and Canada 

and elevations are referenced to the International 

Great Lakes Datum of 1985. It is important to note 

that Lake Michigan and Lake Huron are 

hydraulically treated as one lake due to their 

connection at the Straits of Mackinac. The period 

of record used for each of the lakes includes the 

years 1918 to 2016. All 2017 water levels will be 

officially coordinated and added to the historical 

record in the spring of 2018. 

The Great Lakes are very large and behave 

differently from smaller, inland lakes. In general, 

Great Lakes water levels do not substantially 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 trends typically cause 

an annual pattern of rising and falling of Great 

Lakes water levels. Each of the Great Lakes 

typically 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: 

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.

Warm Winter, Wet Spring 2017

In the beginning of 2017, water levels across the 

Great Lakes remained fairly close to water levels 

Great Lakes

Update
Vol. 199 Great Lakes Update February 2018

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experienced in 2016. However, in the spring of

2017 water levels began to separate themselves 

and begin a higher track than the previous year’s

levels. In January and February, overall conditions 

were warmer than average. Last February, a week 

of record warmth throughout the basin allowed for 

some early thawing and snowmelt in the basin. 

Figure 1 shows the above normal temperatures 

during the winter, where temperatures were 3 to 7 

degrees Fahrenheit warmer than normal.

 http://www.cpc.ncep.noaa.gov/products/tanal/temp_analyses.php

Figure 1: 90-Day Anomaly in mean 

temperatures during the winter

Figure 2 shows the monthly precipitation during 

2017 for each lake, which indicates the wet spring 

and early summer in the Great Lakes region. In 

March, cold temperatures throughout the basin and 

above average precipitation around the lower lakes 

allowed for snowpack to build especially in the 

Lake Ontario basin where a mid-month snowstorm 

brought 1 to 2 feet of snow to most of the basin.

An exceptionally wet April along with above 

average runoff in May, began larger rises on the

lakes. The Lake Ontario basin experienced record 

high precipitation during the month of May with 

precipitation for the month just shy of a total of 6 

inches. The monthly average for Lake Ontario 

basin precipitation in May is 3.10 inches based on 

the period of record (1900-2016), which was 

surpassed in the first 6 days of May. This led to 

flooding along the Lake Ontario shoreline, shown 

in Figure 3. Lake Erie also had over 5 inches of 

Figure 2: Monthly precipitation of 2017 

compared to monthly average precipitation

rain in May contributing to the steep rise in lake 

level. For Lakes Superior and Michigan-Huron, 

May precipitation was just slightly above average, 

but April and June precipitation was well above 

average. This led to a rise in lake levels during 

these months that was greater than average and 

pushed lake levels above 2016 levels. 

Figure 3: Flooding in Sackets Harbor, NY at 

the end of May 2017
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Figure 4: Lake Superior Water Levels

Figure 5: Lake Superior Residual Net Basin Supply

Lake Superior

Figure 4 shows the 2017 water levels of Lake 

Superior compared with the 2016 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 (or low water 

datum), which represents the value at zero. Chart 

datum for Lake Superior is 601.1 ft. The solid line

in Figure 4 represents the daily 2017 water levels 

and the dashed line shows the 2016 levels. The 

LTA levels for each month are shown by the solid 

circles. Figure 5 shows residual net basin supply 

(NBS), which accounts for the contribution of 

precipitation, runoff, and evaporation to the lake. 
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Lake Superior started the year below water levels 

of 2016, but above the LTA levels. However, 

consecutive months of above average NBS in 

April, May, and June, led to a significant rise in 

Lake Superior water levels that brought water 

levels above 2016 levels. 

Lake Superior’s water level continued to rise until 

October when it reached its peak monthly average

for the year at 603.05 feet. It’s typical from 

September to October for Lake Superior to begin 

its seasonal decline, but October experienced high 

monthly NBS, which was also preceded by above 

average supplies in August and September. The 

period of higher than average NBS between 

August and October was a result of above average 

precipitation and runoff during this time. 

Since June, Lake Superior monthly average levels 

have been 9 to 13 inches above LTA and 2 to 4 

inches below its monthly record high water levels. 

Subsequently, the monthly average water levels 

from October to December were the highest water 

levels that have occurred since record high levels 

in 1985. 

Lake Michigan-Huron

Lake Michigan-Huron water levels remained 

above average throughout 2017, shown in Figure 

6. The lake started off the year below 2016 levels, 

but by June 2017 water levels surpassed 2016 

levels and it remained that way through December. 

Lake Michigan-Huron was 3 to 4 inches below 

2016 levels from January to April, but finished the 

year in December 11 inches above the 2016 level 

and 18 inches above the LTA level. The water 

levels from July to November were the highest 

water levels since the last period of high water in 

1997. The December 2017 water level of 580.02 

feet was the highest water level in this month since 

the record high December level in 1986. 

From January (578.97 ft.) to August (580.71 ft.), 

Lake Michigan-Huron rose 21 inches - 10 inches 

more than the average rise that typically takes 

place from February to July. Figure 7 illustrates 

that during the time period from January to July 

NBS was above the LTA, and especially high 

during April, May, and June, which helped to 

amplify the seasonal rise on the lake. 

Figure 6: Lake Michigan-Huron Water Levels
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Figure 7: Lake Michigan-Huron Residual Net Basin Supply

Lake St. Clair

Figure 8 shows the water levels of Lake St. Clair 

in 2017 compared to 2016 and the LTA levels. 

From January to April, the lake was within 2 

inches of 2016 levels. However, in May the water 

level climbed to 4 inches above its 2016 level and 

19 inches above the LTA. Since May, water levels 

have continued to stay above 2016 levels and 18 to 

21 inches above LTA levels. Lake St. Clair 

reached its seasonal low in December of 2016 at 

574.54 feet. During 2017, the lake rose 23 inches 

to its seasonal peak in July to 576.44 feet. The 

average seasonal rise on Lake St. Clair is 16 

inches, which typically occurs between February 

and July, but above average NBS in January and 

February contributed to an earlier rise in 2017.

Figure 8: Lake St. Clair Water Levels
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Lake Erie

Lake Erie also experienced similar water levels to 

2016 in the beginning of 2017, and in early May 

saw a rapid rise in water level (Figure 9). In May, 

NBS was well above average and a precipitation 

event early in the month caused the level to rise 

quickly over a few days. Since May, Lake Erie 

water levels have been 6 to 11 inches above 2016 

levels and 16 to 20 inches above LTA levels. 

The seasonal rise on Lake Erie took place between 

December 2016 and June of 2017, rising 26 inches

from 571.42 ft. to 573.59 ft. The typical rise 

between December and June is 14 inches. The 

remarkable rise of 26 inches was 12 inches more

than average because of the wet spring that caused 

water levels to jump significantly. Precipitation 

and runoff were much greater than average in 

January and May resulting in higher than average 

NBS, as shown in Figure 10. 

In November, NBS was also well above average as 

a result of wetter than normal conditions in the 

basin. These generally wet conditions since the 

spring kept the lake above 2016 and LTA levels. 

Figure 9: Lake Erie Water Levels

Figure 10: Lake Erie Residual Net Basin Supply
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Lake Ontario

Figure 11 shows Lake Ontario water levels relative 

to the chart datum of 243.3 ft. Lake Ontario started 

the year within 1 inch of 2016 water levels, but in 

April Lake Ontario began a steep rise that would 

lead to record high water levels in the spring and 

early summer. 

From December 2016 to June 2017 the level of 

Lake Ontario rose 53 inches. This was the largest 

seasonal rise on the lake in the period of record 

(1918-2016). Above average precipitation of over 

10 inches between April and May (Figure 2) along 

with rapid snowmelt during April due to warmer 

than normal temperatures led to the rapid rise in 

water levels during April and May. Figure 12

shows the 2017, 2016, and LTA NBS for Lake 

Ontario. Overall, well above average NBS 

between April and July led to record high water 

levels in May, June, and July. This can be seen in 

Figure 11 where the line representing 2017 water 

levels surpasses the horizontal lines representing 

record high water levels during these three months. 

In May, the monthly mean level of 248.69 feet 

surpassed the previous May record high in 1973 by 

3 inches. The highest monthly average level for all 

months in the period of record occurred in June at 

248.72 feet, surpassing the old record by 2 inches, 

which occurred in 1952. During this time of record 

high water levels, flooding and erosion were 

significant concerns along the Lake Ontario 

shoreline (Figure 3) as well as along the St. 

Lawrence River and in the Ottawa River basin.

The seasonal decline on Lake Ontario between 

June 2017 and December 2017 was 41 inches, 

which is almost double the average decline during 

this time period. In June, July, and August, 

monthly averaged outflows out of Lake Ontario 

into the St. Lawrence River were above monthly 

record highs. 

Figure 11: Lake Ontario Water Levels
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Figure 12: Lake Ontario Residual Net Basin Supply

More Information

Update articles are included periodically in the 

Monthly Bulletins highlighting topics and 

explanations relevant to Great Lakes water levels. 

February’s Monthly Bulletin typically includes an 

annual summary from the year before.

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 each Thursday. Additionally, a one 

year Great Lakes Water Level Outlook is produced 

once every three months. All forecast products are 

located here:

http://www.lre.usace.army.mil/Missions/GreatLakesInform

ation/GreatLakesWaterLevels/WaterLevelForecast.aspx

The Detroit District also has a Facebook page 

which can be found here:

https://www.facebook.com/pages/Detroit-District-USArmy-Corps-of-Engineers/144354390916

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