Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2015

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2016

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

1952

JUL

1947

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2017

JAN

1946

1935

FEB

1952

1936

MAR

19521935

APR

19731935

MAY

19731935

JUN

19521935

JUL

19471934

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

18

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

2015

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2016

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

2017

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

18

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

2015

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2016

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

2017

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

18

JAN

19861936

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

602.85183.75

602.66

183.69603.08183.82

1950

600.26182.96

1926

602.07

183.51

MichHuron

580.68176.99580.18176.84581.99177.39

1986

576.71

175.78

1964

579.30

176.57

St.

Clair

576.44

175.70

575.75175.49

577.20

175.93

1986

572.51

174.50

1934

574.77175.19

Erie

573.52

174.81

572.64174.54574.25175.03

1986

569.06

173.45

1934

571.92174.32

Ontario

248.33

75.69

245.90

74.95

248.23

75.66

1947

243.24

74.14

1934

246.06

75.00

JULY MEAN LAKE LEVELS

(IGLD 1985)

* 2017 Ft.

M.

2016 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2016

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 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 2017

According to preliminary estimates, precipitation during the month of July was below average for the Great Lakes 

basin. Lake Ontario was the only lake that received above average precipitation during July, receiving 114% of 

average precipitation. Lakes Superior, Michigan-Huron, and Erie received 73%, 90%, and 92% of average 

precipitation, respectively. The net basin supplies were above average for all of the lakes, except Lake Superior. The 

outflows for July were above average for all lakes and for the second consecutive month, Lake Ontario’s preliminary 

average monthly outflow estimate is a record high outflow based on the period of record3. 

The July monthly mean levels for all the lakes were above their July long-term average levels and above last year’s 

July levels. From June to July, Lake Superior rose 3 inches, Lake Michigan-Huron rose 4 inches, and Lake St. Clair 

rose 2 inches. Lake Erie declined less than an inch and Lake Ontario declined 5 inches in the last month. However, 

Lake Ontario’s July water level of 248.33 feet is the highest July monthly mean water level recorded based on the 

period of record (1918-2016). 

PRELIMINARY PRECIPITATION (INCHES)

BASIN

July 12-Month Comparison

2017 Average Diff. % of 

Average

Last 12 

months 

Average Diff. % of 

(1900-2014) (1900-2014) Average

Superior 2.41 3.28 -0.87 73 33.41 30.52 2.89 109

Michigan-Huron 2.74 3.03 -0.29 90 36.65 32.57 4.08 113

Erie 3.13 3.41 -0.28 92 39.34 35.65 3.69 110

Ontario 3.64 3.19 0.45 114 41.90 35.87 6.03 117

Great Lakes 2.83 3.16 -0.33 90 36.77 32.76 4.01 112

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

2017 Average

(1900-2008) 2017 Average3(1900-2008)

Superior 118,000 129,000 114,000 81,000

Michigan-Huron 151,000 128,000 214,000 195,000

Erie 34,000 7,000 251,000 209,000

Ontario 57,000 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