Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

2021

MAY

2017

JUN

2019

JUL

2019

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2022

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

2017

1935

JUN

2019

1935

JUL

2019

1934

AUG

1947

1934

SEP

1947

1934

OCT

1945

1934

NOV

1945

1934

DEC

1945

1934

2023

JAN

1946

1935

FEB

1952

1936

MAR

1952

1935

APR

1973

1935

MAY

2017

1935

JUN

2019

1935

JUL

2019

1934

AUG

1947

1934

SEP

1947

1934

OCT

1945

1934

LAKE ONTARIO

CHART DATUM 243.3 FEET (74.2 METERS)

Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

+ 6

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

+ 1.8

2021

MAY

2020

JUN

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1986

NOV

1986

DEC

1986

2022

JAN

1987

FEB

2020

MAR

2020

APR

2020

MAY

2020

1934

JUN

2019

1934

JUL

2019

1934

AUG

2019

1934

SEP

2019

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2023

JAN

1987

1935

FEB

2020

1936

MAR

2020

1934

APR

2020

1934

MAY

2020

1934

JUN

2019

1934

JUL

2019

1934

AUG

2019

1934

SEP

2019

1934

OCT

1986

1934

LAKE ERIE

CHART DATUM 569.2 FEET (173.5 METERS)

Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

2021

MAY

2020

JUN

2020

JUL

2019

AUG

2020

SEP

2020

OCT

1986

NOV

1986

DEC

1986

2022

JAN

2020

FEB

1986

MAR

2020

APR

2020

MAY

2020

1934

JUN

2020

1934

JUL

2019

1934

AUG

2020

1934

SEP

2020

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2023

JAN

2020

1936

FEB

1986

1926

MAR

2020

1934

APR

2020

1926

MAY

2020

1934

JUN

2020

1934

JUL

2019

1934

AUG

2020

1934

SEP

2020

1934

OCT

1986

1934

LAKE ST. CLAIR

CHART DATUM 572.3 FEET (174.4 METERS)

Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

2021

MAY

2020

JUN

2020

JUL

2020

AUG

2020

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2022

JAN

2020

FEB

2020

MAR

2020

APR

2020

MAY

2020

1964

JUN

2020

1964

JUL

2020

1964

AUG

2020

1964

SEP

1986

1964

OCT

1986

1964

NOV

1986

1964

DEC

1986

2012

2023

JAN

2020

2013

FEB

2020

1964

MAR

2020

1964

APR

2020

1964

MAY

2020

1964

JUN

2020

1964

JUL

2020

1964

AUG

2020

1964

SEP

1986

1964

OCT

1986

LAKES MICHIGAN-HURON 1964

CHART DATUM 577.5 FEET (176.0 METERS)

Ft.

-1

0

+ 1

+ 2

M.

-0.3

0

+ 0.3

+ 0.6

2021

MAY

2019

JUN

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1985

NOV

1985

DEC

1985

2022

JAN

2020

FEB

2020

MAR

1986

APR

1986

MAY

2019

1926

JUN

2019

1926

JUL

2019

1926

AUG

2019

2007

SEP

2019

2007

OCT

1985

1925

NOV

1985

1925

DEC

1985

1925

2023

JAN

2020

1926

FEB

2020

1926

MAR

1986

1926

APR

1986

1926

MAY

2019

1926

JUN

2019

1926

JUL

2019

1926

AUG

2019

2007

SEP

2019

2007

OCT

1985

1925

LAKE SUPERIOR

CHART DATUM 601.1 FEET (183.2 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH RESPECTIVE LAKE

Superior

601.97

183.48

601.18

183.24

602.62

183.68

1986

599.48

182.72

1926

601.28

183.27

MichHuron

579.27

176.56

579.59

176.66

581.66

177.29

2020

576.15

175.61

1964

578.77

176.41

St.

Clair

575.52

175.42

575.46

175.40

577.13

175.91

2020

571.92

174.32

1926

574.38

175.07

Erie

572.97

174.64

572.80

174.59

574.31

175.05

2020

568.83

173.38

1934

571.69

174.25

Ontario

246.49

75.13

246.49

75.13

248.20

75.65

1973

242.88

74.03

1935

245.70

74.89

APRIL MEAN LAKE LEVELS

(IGLD 1985)

* 2023 Ft.

M.

2022 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional

** Average, Maximum and Minimum for period 1918-2022

LEGEND

LAKE LEVELS

RECORDED

PROJECTED

AVERAGE **

MAXIMUM **

1985

1985

1973 1973

MINIMUM **

1936

1934

1926 1934

MAY 2023

US Army Corps

of Engineers

Detroit District

MONTHLY BULLETIN OF

LAKE LEVELS FOR THE

GREAT LAKES

Monthly mean water levels for the previous year and the

current year to date are shown as a solid line 

on the hydrographs. A projection for the next

six months is given as a dashed line. This 

projection is based on the present condition 

of the lake basin and anticipated future 

weather. The shaded area shows a range of

possible levels over the next six months 

dependent upon weather variations. Current

and projected levels (solid and dashed lines) 

can be compared with the 1918-2022 average

levels (dotted line) and extreme levels 

(shown as bars with their year of occurrence).

The legend below further identifies the 

information on the hydrographs. 

The levels on the hydrographs are shown in

both feet and meters above (+) or below (-) 

Chart Datum. Chart Datum, also known as 

Low Water Datum, is a reference plane on 

each lake to which water depth and Federal 

navigation improvement depths on navigation 

charts are referred.

All elevations and plots are referenced to the

International Great Lakes Datum 1985 (IGLD 1985). 

IGLD 1985 has its zero base at Rimouski, Quebec 

near the mouth of the St. Lawrence River 

(approximate sea level). 

Visit our website for more information:

https://www.lre.usace.army.mil/greatlakes
 Information

Recorded monthly mean water levels in this bulletin are results from a representative network of water level gages 

on each lake (see cover map). Providers of these data are U.S. Department of Commerce, NOAA, National Ocean 

Service, and Integrated Science Data Management, Department of Fisheries and Oceans, Canada. Detroit District, 

Corps of Engineers and Environment and Climate Change Canada derive historic and projected lake levels under 

auspices of Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data.

The Corps makes the bulletin monthly as a public service. The Corps also, on a weekly basis publishes online the 

Great Lakes, Connecting Channels and St. Lawrence River Water Levels and Depths, which supplies a forecast of 

depths in connecting rivers between Great Lakes and International Section of St. Lawrence River. This Monthly 

Bulletin of the Lake Levels for the Great Lakes is available in full color on the internet at 

https://www.lre.usace.army.mil/Missions/GreatLakesInformation.aspx. For questions, email hhpm@usace.army.mil

or call 1-888-694-8313 and select option 1.

Great Lakes Basin Hydrology

April 2023 

Great Lakes precipitation was around 25% above average for April. This was the 2nd consecutive April in which Lake 

Superior experienced precipitation that was over 60% above average. The individual lake basins of Michigan-Huron 

and Ontario also received above average precipitation in April, while the Lake Erie basin experienced below average 

precipitation. Over the past 12 months, overall precipitation has been near to below average in each of the lake 

basins. Provisional statistics show water supplies were substantially above average on Lake Superior, while Lakes 

Michigan-Huron and Ontario also received above average supplies. Water supplies were below average on Lake 

Erie. The connecting channel outflows for each lake remained above average in April. 

All of the lakes experienced a rise in water levels during April. The monthly mean levels of Lakes Superior, MichiganHuron, St. Clair, Erie, and Ontario climbed 2, 5, 5, 4, and 10 inches, respectively, from March to April. The current

Great Lakes water levels 6-month forecast projects continued rise in levels of Lakes Superior, Michigan-Huron, and 

Ontario. During May, Lake St. Clair is projected to remain near its April level, while Lake Erie is expected to begin

its seasonal decline. 

PRECIPITATION (INCHES)

BASIN

April 12-Month Comparison

2023 Average Diff. % of 

Average

Average 

Last 12 

Months

Average Diff. % of 

(1900-2020) (1900-2020) Average

Superior 3.35 2.05 1.30 163 29.10 30.67 -1.57 95

Michigan-Huron 3.17 2.72 0.45 117 29.37 32.99 -3.62 89

Erie 2.70 3.23 -0.53 84 31.81 35.98 -4.17 88

Ontario 4.24 2.99 1.25 142 35.16 36.42 -1.26 97

Great Lakes 3.28 2.64 0.64 124 30.31 33.11 -2.80 92

Lake

April WATER SUPPLIES1 (cfs) March OUTFLOW2 (cfs)

2023 Average3

(1900-2008) 2023 Average3(1900-2008)

Superior 275,000 151,000 76,000 68,000

Michigan-Huron 411,000 286,000 196,000 182,000

Erie 55,000 68,000 246,000 207,000

Ontario 97,000 91,000 278,000 250,000

Notes: Values (excluding averages) are based on preliminary computations; cfs denotes cubic feet per second. 

1 Net basin supply is the net result of precipitation falling on the lake, runoff from precipitation falling on the land which flows to 

the lake, and evaporation from the lake. Negative net basin supply denotes evaporation exceeded runoff and precipitation. 

The net total supply can be found by adding the net basin supply and the outflow from the upstream lake. 

2 Does not include diversions. 

3 Lake Ontario average water supplies and average outflows are based on period of record 1900-2005