Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2011

AUG

1947

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2012

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

1952

JUL

1947

AUG

19471934

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2013

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

14

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

2011

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2012

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

2013

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

14

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

2011

AUG

1986

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2012

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

2013

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

14

JAN

19861936

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

601.61

183.37601.38

183.30

603.08183.82

1950

600.26182.96

1926

602.03

183.50

MichHuron

577.72176.09

577.56

176.04581.99177.39

1986

576.71

175.78

1964

579.30

176.57

St.

Clair

574.48

175.10

573.95174.94

577.20

175.93

1986

572.51

174.50

1934

574.74175.18

Erie

572.01

174.35571.33174.14574.25175.03

1986

569.06

173.45

1934

571.88

174.31

Ontario

246.52

75.14

245.37

74.79

248.23

75.66

1947

243.24

74.14

1934

246.03

74.99

JULY MEAN LAKE LEVELS

(IGLD 1985)

* 2013 Ft.

M.

2012 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2012

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 publishes the "Great Lakes, Connecting 

Channels and St. Lawrence River Water Levels and Depths,” weekly, 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 2013

Most of the Great Lakes basin received above average precipitation for the month of July. The Superior basin 

received above average precipitation in July at 161%, of average. The Michigan-Huron basin, however, received 

average precipitation. The Erie and Ontario basins received 149% and 108% of average precipitation, 

respectively, in July. Overall, the Great Lakes basin received above average precipitation last month. The net 

basin supply of water to the lakes was above average in July, with the exception of Michigan-Huron’s net basin 

supply which was below average. The outflows from lakes Superior and Michigan-Huron were below average 

while the outflow from Lake Erie was near average. The outflow from Lake Ontario was above average. The 

tables below list July precipitation and water supplies for the Great Lakes basin. 

The water levels of all of the Great Lakes are starting to round out their seasonal rise. Each of the lakes rose 

between 2 and 5 inches from June’s monthly mean to July’s monthly mean. A comparison of July’s monthly mean 

lake levels to long-term average (1918-2012) shows Lakes Superior, Michigan-Huron and St. Clair were 5, 19 and 

3 inches below average, respectively. Lakes Erie and Ontario were 2 and 6 inches above LTA, respectively. 

Boaters should be aware of hazards to navigation due to continued below average water levels on the upper lakes. 

 

PRECIPITATION (INCHES) 

BASIN 

July 12-Month Comparison 

2013 Average Diff. % of 

Average 

Last 12 

months 

Average Diff. % of 

(1900-2010) (1900-2010) Average 

Superior 5.27 3.27 2.00 161 29.08 30.46 -1.38 95 

Michigan-Huron 3.03 3.03 0.00 100 33.87 32.44 1.43 104 

Erie 5.04 3.39 1.65 149 38.42 35.43 2.99 108 

Ontario 3.44 3.18 0.26 108 35.99 35.73 0.26 101 

Great Lakes 3.96 3.16 0.80 125 33.30 32.64 0.66 102 

 

 LAKE July Net Basin Supplies1

 (cfs) July Outflows2 (cfs) 

2013 Average3

(1900-2008) 2013 Average3(1900-2008)

Superior 225,000 129,000 77,000 81,000 

Michigan-Huron 94,000 128,000 168,000 195,000 

Erie 38,000 7,000 208,000 209,000 

Ontario 28,000 24,000 264,000 261,000 

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