Ft.

-1

0

+ 1

+ 2

+ 3

+ 4

+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9

+ 1.2

+ 1.5

2018

MAY

2017

JUN

2019

JUL

2019

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2019

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

2020

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

2018

MAY

2019

JUN

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1986

NOV

1986

DEC

1986

2019

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

2019

1934

JUN

2019

1934

JUL

2019

1934

AUG

2019

1934

SEP

2019

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2020

JAN

1987

1935

FEB

1987

1936

MAR

1986

1934

APR

1985

1934

MAY

2019

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

2018

MAY

2019

JUN

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1986

NOV

1986

DEC

1986

2019

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

2019

1934

JUN

2019

1934

JUL

2019

1934

AUG

2019

1934

SEP

2019

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2020

JAN

1986

1936

FEB

1986

1926

MAR

1986

1934

APR

1986

1926

MAY

2019

1934

JUN

2019

1934

JUL

2019

1934

AUG

2019

1934

SEP

2019

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

2018

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2019

JAN

1987

FEB

1986

MAR

1986

APR

1986

MAY

1986

1964

JUN

1986

1964

JUL

1986

1964

AUG

1986

1964

SEP

1986

1964

OCT

1986

1964

NOV

1986

1964

DEC

1986

2012

2020

JAN

1987

2013

FEB

1986

1964

MAR

1986

1964

APR

1986

1964

MAY

1986

1964

JUN

1986

1964

JUL

1986

1964

AUG

1986

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

2018

MAY

2019

JUN

2019

JUL

2019

AUG

2019

SEP

2019

OCT

1985

NOV

1985

DEC

1985

2019

JAN

1986

FEB

1986

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

2020

JAN

1986

1926

FEB

1986

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

602.43

183.62

602.40

183.61

602.62

183.68

1986

599.48

182.72

1926

601.25

183.26

MichHuron

581.69

177.30

580.58

176.96

581.46

177.23

1986

576.15

175.61

1964

578.71

176.39

St.

Clair

577.13

175.91

576.44

175.70

576.84

175.82

1986

571.92

174.32

1926

574.34

175.06

Erie

574.31

175.05

573.59

174.83

574.08

174.98

1985

568.83

173.38

1934

571.65

174.24

Ontario

247.11

75.32

246.56

75.15

248.20

75.65

1973

242.88

74.03

1935

245.70

74.89

APRIL MEAN LAKE LEVELS

(IGLD 1985)

* 2020 Ft.

M.

2019 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional

** Average, Maximum and Minimum for period 1918-2019

LEGEND

LAKE LEVELS

RECORDED

PROJECTED

AVERAGE **

MAXIMUM **

1985

1985

1973 1973

MINIMUM **

1936

1934

1926 1934

MAY 2020

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 1918-2019 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 

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

Great Lakes Basin Hydrology

April 2020

Preliminary estimates indicate that precipitation for the Great Lakes basin was below average in April. For the 

individual lake basins, precipitation was below average on Lakes Superior and Erie, while a very wet end of the 

month brought precipitation to near average for Lakes Michigan-Huron and Ontario. Water supplies for all of the 

lakes were below average in April. Despite water supply being below average, given the high water conditions 

outflows remain high throughout the basin and were above average in April. The preliminary outflow estimates

through the St. Clair River, Detroit River, and the Niagara River were above record highs for the month of April.

For the month of April, new record high monthly mean water levels were set on Lakes Michigan-Huron, St. Clair, and 

Erie. These levels surpassed their previous records by 3 to 4 inches, which were set in 1986 on Lakes MichiganHuron and St. Clair and in 1985 on Lake Erie. All of the lakes experienced a rise in water levels from March to April.

Lake Superior rose 2 inches from March to April, while Lakes Michigan-Huron and St. Clair both rose 3 inches. Lakes 

Erie and Ontario also rose by 4 and 6 inches, respectively, from March to April. 

PRECIPITATION (INCHES)

BASIN

April 12-Month Comparison

2020 Average Diff. % of 

Average

Last 12 

months 

Average Diff. % of 

(1900-2017) (1900-2017) Average

Superior 1.37 2.05 -0.68 67 28.49 30.59 -2.10 93

Michigan-Huron 2.66 2.68 -0.02 99 33.72 32.52 1.20 104

Erie 2.16 3.19 -1.03 68 35.08 35.55 -0.47 99

Ontario 2.95 2.95 0.00 100 35.89 35.83 0.06 100

Great Lakes 2.26 2.60 -0.34 87 32.66 32.76 -0.10 100

 LAKE April WATER SUPPLIES1 (cfs) April OUTFLOW2 (cfs)

2020 Average

(1900-2008) 2020 Average3(1900-2008)

Superior 99,000 150,000 80,000 68,000

Michigan-Huron 272,000 284,000 254,000 182,000

Erie 32,000 67,000 285,000 207,000

Ontario 57,000 93,000 315,000 251,000

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