Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2017

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2018

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

2017

JUN

2017

JUL

2017

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2019

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

MAY

20171935

JUN

20171935

JUL

20171934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

20

JAN

1946

1935

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

2017

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2018

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

1986

JUN

1986

JUL

1986

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2019

JAN

19871935

FEB

1987

1936

MAR

1986

1934

APR

19851934

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

20

JAN

19871935

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

2017

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2018

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

1986

JUN

1986

JUL

1986

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2019

JAN

19861936

FEB

19861926

MAR

1986

1934

APR

19861926

MAY

1986

1934

JUN

1986

1934

JUL

1986

1934

AUG

1986

1934

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

20

JAN

19861936

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

603.22

183.86

602.53183.65603.08183.82

1950

600.26182.96

1926

602.07

183.51

MichHuron

581.92177.37580.64176.98581.99177.39

1986

576.71

175.78

1964

579.33176.58

St.

Clair

577.56

176.04576.48

175.71

577.20

175.93

1986

572.51

174.50

1934

574.80175.20

Erie

574.57175.13

573.56

174.82574.25175.03

1986

569.06

173.45

1934

571.95174.33

Ontario

248.69

75.80

246.26

75.06

248.33

75.69

2017

243.24

74.14

1934

246.10

75.01

JULY MEAN LAKE LEVELS

(IGLD 1985)

* 2019 Ft.

M.

2018 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2018

1985

1985

1973 1973

1936

1934

1926 1934

LAKE ONTARIO

LAKE ERIE

LAKE ST. CLAIR

LEGEND

LAKE LEVELS

RECORDEDPROJECTEDAVERAGE **MAXIMUM **MINIMUM **

The levels on the hydrographs are shown inboth 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

July 2019

Preliminary estimates indicate the Great Lakes basin received below average precipitation in the month of July. Lake 

Erie received above average precipitation at 110% of average. The rest of the lakes received less than average 

precipitation, at 73% to 85% of average. While precipitation was below average, water supplies were near average 

for Superior, Michigan-Huron and Erie, and above normal for Ontario. The Lake Michigan-Huron basin and Erie 

basin predominately experienced above normal runoff, while Superior and Ontario experienced near normal runoff. 

Outflows from all lakes continued to be substantially above average during the month of July, with preliminary 

estimates indicating that outflows through the St. Clair River, Detroit River, and Niagara River were all above their 

record high outflows for July. 

In 2019, Lakes Superior, St. Clair, Erie, and Ontario experienced their highest July monthly mean water level dating 

back to 1918, the beginning of their period of record. From June to July, the monthly mean levels of Lakes Superior, 

Michigan-Huron and St. Clair rose, while Lakes Erie and Ontario’s monthly mean levels declined. The current 6-

month forecast indicates monthly mean water levels for August will meet or surpass record high August levels on 

Lakes Superior, St. Clair and Erie. 

 

PRECIPITATION (INCHES) 

BASIN 

July 12-Month Comparison 

2019 Average Diff. % of 

Average 

Average Last 

12 Months 

Average Diff. % of 

(1900-2016) (1900-2016) Average 

Superior 2.69 3.28 -0.59 82 29.48 30.58 -1.10 96 

Michigan-Huron 2.20 3.03 -0.83 73 34.98 32.55 2.43 107 

Erie 3.72 3.39 0.33 110 38.81 35.62 3.19 109 

Ontario 2.70 3.17 -0.47 85 38.76 35.87 2.89 108 

Great Lakes 2.57 3.16 -0.59 81 34.32 32.77 1.55 105 

 

 LAKE July WATER SUPPLIES1 (cfs) July OUTFLOW2 (cfs) 

2019 Average 

(1900-2008) 2019 Average3(1900-2008)

Superior 138,000 129,000 112,000 81,000 

Michigan-Huron 140,000 128,000 249,000 195,000 

Erie 8,000 7,000 275,000 209,000 

Ontario 32,000 24,000 367,000 261,000 

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