Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2016

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2017

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

2017

JUN

2017

JUL

2017

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2018

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

19

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

2016

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2017

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

2018

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

19

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

2016

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2017

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

2018

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

19

JAN

19861936

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

602.53183.65602.85183.75603.08183.82

1950

600.26182.96

1926

602.07

183.51

MichHuron

580.64176.98580.68176.99581.99177.39

1986

576.71

175.78

1964

579.33176.58

St.

Clair

576.48

175.71

576.44

175.70577.20

175.93

1986

572.51

174.50

1934

574.80175.20

Erie

573.56

174.82573.52

174.81

574.25175.03

1986

569.06

173.45

1934

571.95174.33

Ontario

246.26

75.06

248.33

75.69

248.33

75.69

2017

243.24

74.14

1934

246.06

75.00

JULY MEAN LAKE LEVELS

(IGLD 1985)

* 2018 Ft.

M.

2017 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2017

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 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) 226-6442 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 2018

According to preliminary precipitation estimates, precipitation within the Great Lakes basin was about 20% below 

average in July. Lakes Superior, Erie, and Ontario received 89%, 85%, and 93% of their average July precipitation, 

while Lake Michigan-Huron received just 68% of its normal July precipitation. In July, Lake Superior received above 

average net basin supply (NBS), while Lake Michigan-Huron received well below average NBS. Lake Erie and Lake 

Ontario also received somewhat below average NBS in July.

All of the lakes remained above their long-term average water levels in July. Lake Superior’s monthly mean level this 

July was 4 inches below its level of a year ago, while Lake Michigan-Huron was close to its level of last July. Lakes 

St. Clair and Erie July levels were also similar to the July 2017 levels, while Lake Ontario’s level was 25 inches below 

last year’s record high July level. From June to July, Lake Superior’s level rose by 4 inches while Lakes MichiganHuron and St. Clair’s July levels were close to their June levels. Lakes Erie and Ontario fell by 3 and 6 inches, 

respectively, from June to July.

PRELIMINARY PRECIPITATION (INCHES)

BASIN

July 12-Month Comparison

2018 Average Diff. % of 

Average

Average Last 

12 Months

Average Diff. % of 

(1900-2016) (1900-2016) Average

Superior 2.93 3.28 -0.35 89 29.56 30.58 -1.02 97

Michigan-Huron 2.06 3.03 -0.97 68 28.85 32.55 -3.70 89

Erie 2.87 3.39 -0.52 85 32.71 35.62 -2.91 92

Ontario 2.94 3.17 -0.23 93 32.95 35.87 -2.92 92

Great Lakes 2.50 3.16 -0.66 79 29.95 32.77 -2.82 91

 LAKE July Net Basin Supplies1 (cfs) July Outflows2 (cfs)

2018

Average

(1900-2008) 2018

Average3

(1900-2008)

Superior 148,000 129,000 88,000 81,000

Michigan-Huron 45,000 128,000 209,000 195,000

Erie 1,000 7,000 246,000 209,000

Ontario 10,000 24,000 311,000 261,000

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