Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

2019

JUL

2019

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2020

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

2017

JUN

2019

JUL

2019

1934

AUG

1947

1934

SEP

1947

1934

OCT

1945

1934

NOV

1945

1934

DEC

1945

1934

2021

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

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

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1986

NOV

1986

DEC

1986

2020

JAN

1987

FEB

2020

MAR

2020

APR

2020

MAY

2020

JUN

2019

JUL

2019

1934

AUG

2019

1934

SEP

2019

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2021

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

LAKE ERIE 1934

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

2019

JUL

2019

AUG

2020

SEP

2020

OCT

1986

NOV

1986

DEC

1986

2020

JAN

2020

FEB

1986

MAR

2020

APR

2020

MAY

2020

JUN

2020

JUL

2019

1934

AUG

2020

1934

SEP

2020

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2021

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

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

2019

JUL

2020

AUG

2020

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2020

JAN

2020

FEB

2020

MAR

2020

APR

2020

MAY

2020

JUN

2020

JUL

2020

1964

AUG

2020

1964

SEP

1986

1964

OCT

1986

1964

NOV

1986

1964

DEC

1986

2012

2021

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

LAKES MICHIGAN-HURON

CHART DATUM 577.5 FEET (176.0 METERS)

Ft.

-1

0

+ 1

+ 2

M.

-0.3

0

+ 0.3

+ 0.6

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1985

NOV

1985

DEC

1985

2020

JAN

2020

FEB

2020

MAR

1986

APR

1986

MAY

2019

JUN

2019

JUL

2019

1926

AUG

2019

2007

SEP

2019

2007

OCT

1985

1925

NOV

1985

1925

DEC

1985

1925

2021

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 LAKE SUPERIOR

CHART DATUM 601.1 FEET (183.2 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH RESPECTIVE LAKE

Superior

602.20

183.55

602.69

183.70

603.15

183.84

2019

599.90

182.85

1926

601.87

183.45

MichHuron

580.48

176.93

582.19

177.45

582.19

177.45

2020

576.64

175.76

1964

579.30

176.57

St.

Clair

576.18

175.62

577.49

176.02

577.49

176.02

2020

572.34

174.45

1934

574.80

175.20

Erie

573.20

174.71

574.48

175.10

574.61

175.14

2019

569.06

173.45

1934

572.05

174.36

Ontario

245.11

74.71

247.01

75.29

249.05

75.91

2019

243.41

74.19

1935

246.29

75.07

JUNE MEAN LAKE LEVELS

(IGLD 1985)

* 2021 Ft.

M.

2020 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional

** Average, Maximum and Minimum for period 1918-2020

LEGEND

LAKE LEVELS

RECORDED

PROJECTED

AVERAGE **

MAXIMUM **

1985

1985

1973 1973

MINIMUM **

1936

1934

1926 1934

JULY 2021

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 1918-2020 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 shown in this bulletin 

are referenced to 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 derived from a representative network of water level gages 

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

Ocean Service, and Integrated Science Data Management, Department of Fisheries and Oceans, Canada. The 

Detroit District, Corps of Engineers and Environment and Climate Change Canada derive historic and projected lake 

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

This bulletin is produced 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 provides a forecast of depths 

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

Monthly Bulletin of the Lake Levels for the Great Lakes may be obtained free of charge by writing to the address 

shown on the front cover, by calling (313) 226-6441 or emailing hhpm@usace.army.mil. Notices of change of 

address should include the name of the publication. This information is available on the internet at 

https://www.lre.usace.army.mil/Missions/GreatLakesInformation.aspx.

Great Lakes Basin Hydrology

June 2021

The Great Lakes basin received slightly above average precipitation in June. The month of June was predominantly 

dry until the last weekend of the month when a significant amount of rain fell in central and eastern portions of the 

basin. All the individual lake basins experienced near or above average precipitation in June, except Lake Superior, 

due to the large amount of rain that occurred toward the end of the month. The last 12 months of precipitation for all 

lake basins range from 13% to 19% below average. Water supplies for June were below average on all lakes, except 

for Lake Erie. Also, outflows continue to be above average for all lakes. 

From May to June, Lakes Superior and St. Clair rose about 2 inches, while Lake Erie rose 1 inch. Lake MichiganHuron declined 1 inch from May to June and Lake Ontario remained near its May level in June. The 6-month forecast 

projects that Lake Superior will continue its seasonal rise throughout the summer before beginning its seasonal 

decline. Lakes St. Clair, Erie, and Ontario are forecast to begin or continue their seasonal decline from June to July. 

Lake Michigan-Huron has not experienced a seasonal rise this spring and early summer, but the water level is 

forecast to rise slightly from June to July before continuing its decline later this summer. 

PRECIPITATION (INCHES)

BASIN

June 12-Month Comparison

2021 Average Diff. % of 

Average

Last 12 

months 

Average Diff. % of 

(1900-2017) (1900-2017) Average

Superior 2.13 3.31 -1.18 64 24.69 30.59 -5.90 81

Michigan-Huron 4.11 3.19 0.92 129 28.17 32.52 -4.35 87

Erie 4.15 3.50 0.65 119 28.69 35.55 -6.86 81

Ontario 3.07 3.19 -0.12 96 29.12 35.83 -6.71 81

Great Lakes 3.48 3.27 0.21 106 27.25 32.76 -5.51 83

Lake

June WATER SUPPLIES1 (cfs) June OUTFLOW2 (cfs)

2021 Average3

(1900-2008) 2021 Average3(1900-2008)

Superior 127,000 155,000 81,000 77,000

Michigan-Huron 186,000 205,000 215,000 192,000

Erie 41,000 32,000 242,000 216,000

Ontario 28,000 40,000 269,000 263,000

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