Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

2022

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2023

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

2017

JUN

2019

JUL

2019

AUG

1947

1934

SEP

1947

1934

OCT

1945

1934

NOV

1945

1934

DEC

1945

1934

2024

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

NOV

1945

1934

DEC

1945

1934

25

JAN

1946

1935

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

2022

AUG

2019

SEP

2019

OCT

1986

NOV

1986

DEC

1986

2023

JAN

1987

FEB

2020

MAR

2020

APR

2020

MAY

2020

JUN

2019

JUL

2019

AUG

2019

1934

SEP

2019

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2024

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

NOV

1986

1934

DEC

1986

1934

25

JAN

1987

1935 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

2022

AUG

2020

SEP

2020

OCT

1986

NOV

1986

DEC

1986

2023

JAN

2020

FEB

1986

MAR

2020

APR

2020

MAY

2020

JUN

2020

JUL

2019

AUG

2020

1934

SEP

2020

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2024

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

NOV

1986

1934

DEC

1986

1964

25

JAN

2020

1936

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

2022

AUG

2020

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2023

JAN

2020

FEB

2020

MAR

2020

APR

2020

MAY

2020

JUN

2020

JUL

2020

AUG

2020

1964

SEP

1986

1964

OCT

1986

1964

NOV

1986

1964

DEC

1986

2012

2024

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

1964

NOV

1986

1964

DEC

1986

2012

25

JAN

2020

2013

LAKES MICHIGAN-HURON

CHART DATUM 577.5 FEET (176.0 METERS)

Ft.

-1

0

+ 1

+ 2

M.

-0.3

0

+ 0.3

+ 0.6

2022

AUG

2019

SEP

2019

OCT

1985

NOV

1985

DEC

1985

2023

JAN

2020

FEB

2020

MAR

1986

APR

1986

MAY

2019

JUN

2019

JUL

2019

AUG

2019

2007

SEP

2019

2007

OCT

1985

1925

NOV

1985

1925

DEC

1985

1925

2024

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

NOV

1985

1925

DEC

1985

1925

25

JAN

2020

1926

LAKE SUPERIOR

CHART DATUM 601.1 FEET (183.2 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH RESPECTIVE LAKE

Superior

602.10

183.52

602.62

183.68

603.22

183.86

2019

600.26

182.96

1926

602.10

183.52

MichHuron

579.82

176.73

579.72

176.70

582.19

177.45

2020

576.71

175.78

1964

579.40

176.60

St.

Clair

575.89

175.53

575.79

175.50

577.56

176.04

2019

572.51

174.50

1934

574.90

175.23

Erie

572.93

174.63

572.83

174.60

574.57

175.13

2019

569.06

173.45

1934

572.01

174.35

Ontario

246.00

74.98

246.52

75.14

248.69

75.80

2019

243.24

74.14

1934

246.10

75.01

JULY MEAN LAKE LEVELS

(IGLD 1985)

* 2024 Ft.

M.

2023 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional

** Average, Maximum and Minimum for period 1918-2023

LEGEND

LAKE LEVELS

RECORDED

PROJECTED

AVERAGE **

MAXIMUM **

1985

1985

1973 1973

MINIMUM **

1936

1934

1926 1934

AUGUST 2024

US Army Corps

of Engineers

Detroit District

MONTHLY BULLETIN OF

LAKE LEVELS FOR THE

GREAT LAKES

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 1918-2023 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). 
 Information

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

on each lake. 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.lrd.usace.army.mil/Water-Information/Water-Management/Great-Lakes-and-Harbors/Water-LevelForecasts/. For questions, email hhpm@usace.army.mil or call 1-888-694-8313 and select option 1.

Great Lakes Basin Hydrology

July 2024 

Preliminary estimates indicate that precipitation for the month of July was near average for the Great Lakes basin. 

The Lake Superior basin was the only basin to experience below average precipitation at 66% of average. The Lakes 

Michigan-Huron, Erie, and Ontario basins received precipitation that was near to above average, ranging from 106% 

to 119% of average. Over the past 12 months, total precipitation has been near average in each of the lake basins 

except for Lake Superior which has been below average. Provisionally, Lakes Michigan-Huron and Ontario received 

above average water supplies, while Lakes Superior and Erie experienced water supplies below average. Outflows 

through the Great Lakes’ connecting channels were above average in July for all lakes. 

Monthly mean water levels for Lakes Superior, Michigan-Huron, and St. Clair each rose 3 inches from June to July. 

Lake Erie’s monthly mean level stayed close to its June level in July, while Lake Ontario climbed 2 inches. The 

updated Great Lakes water levels 6-month forecast predicts that Lakes Michigan-Huron, St. Clair, Erie, and Ontario 

will begin or resume their seasonal decline from July to August. Lake Superior is forecast to remain near its July 

level in August. 

PRECIPITATION (INCHES)

BASIN

July 12-Month Comparison

2024 Average Diff. % of 

Average

Last 12 

months 

Average Diff. % of 

(1900-2021) (1900-2021) Average

Superior 2.16 3.27 -1.11 66 26.58 30.67 -4.09 87

Michigan-Huron 3.46 3.07 0.39 113 31.57 32.99 -1.42 96

Erie 3.64 3.43 0.21 106 33.40 36.02 -2.62 93

Ontario 3.83 3.23 0.60 119 36.20 36.46 -0.26 99

Great Lakes 3.18 3.19 -0.01 100 30.94 33.11 -2.17 93

Lake

July WATER SUPPLIES1 (cfs) July OUTFLOW2 (cfs)

2024 Average

(1900-2020) 2024 Average(1900-2020)

Superior 56,000 127,000 87,000 81,000

Michigan-Huron 153,000 126,000 205,000 196,000

Erie -9,000 7,000 230,000 214,000

Ontario 52,000 24,000 283,000 264,000

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.