Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2009

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2010

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

1952

JUL

1947

AUG

1947

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2011

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

2012

JAN

1946

1935

FEB

1952

1936

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

2009

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2010

JAN

1987

FEB

1987

MAR

1986

APR

1985

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1934

2011

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

2012

JAN

19871935

FEB

1987

1936

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

2009

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2010

JAN

1986

FEB

1986

MAR

1986

APR

1986

MAY

1986

JUN

1986

JUL

1986

AUG

1986

SEP

1986

1934

OCT

1986

1934

NOV

1986

1934

DEC

1986

1964

2011

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

2012

JAN

19861936

FEB

19861926

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

601.31

183.28601.05

183.20

603.22

183.86

1952

600.43

183.01

2007

602.13183.53

MichHuron

578.22176.24578.22176.24581.99177.39

1986

576.67175.77

1964

579.27

176.56

St.

Clair

574.67

175.16

574.31

175.05

577.10175.90

1986

572.21174.41

1934

574.64175.15

Erie

572.11

174.38571.49174.19573.95174.94

1986

569.00

173.43

1934

571.69174.25

Ontario

245.87

74.94

245.73

74.90

247.97

75.58

1947

242.78

74.00

1934

245.67

74.88

AUGUST MEAN LAKE LEVELS

(IGLD 1985)

* 2011 Ft.

M.

2010 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2010

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. Tables of possible storm-induced rises at key locations on the 

Great Lakes are available on request. 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. These publications can be obtained 

free of charge by writing to the address shown on the front cover, or by calling (313) 226-6441. Notices of change of 

address should include the name of the publication(s). The Internet address http://www.lre.usace.army.mil/glhh

contains this information on the Internet.

Great Lakes Basin Hydrology

August 2011

All of Great Lakes basins experienced above average precipitation in August, with the exception of Lake MichiganHuron. Over the past 12 months, all of the Great Lakes basins have received higher than average precipitation. In 

August, the net supply of water to Lake Superior and Lake Michigan-Huron was below average, while it was above 

average to Lake Erie and Lake Ontario. The tables below list August precipitation and water supply information for all 

Great Lakes basins. 

A comparison of August monthly mean lake levels to long-term average (1918-2010) shows Lakes Superior and 

Michigan-Huron were 10 and 13 inches, respectively, below average. Lake St. Clair was near average, while Lake Erie 

was 5 inches above average in the month of August. Lake Ontario was also 5 inches above average in August. 

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

PRECIPITATION (INCHES)

BASIN

August 12-Month Comparison

2011 Average Diff. % of 

Average

Last 12 

months 

Average Diff. % of 

(1900-2008) (1900-2008) Average

Superior 3.34 3.16 0.18 106 32.08 30.51 1.57 105

Michigan-Huron 2.90 3.11 -0.21 93 34.18 32.44 1.74 105

Erie 3.72 3.22 0.50 116 43.26 35.40 7.86 122

Ontario 4.98 3.11 1.87 160 38.74 35.71 3.03 108

Great Lakes 3.38 3.13 0.25 108 35.44 32.64 2.80 109

 LAKE August WATER SUPPLIES1 (cfs) August OUTFLOW2 (cfs)

2011

Average4

(1900-1989) 2011

Average3

(1900-1999)

Superior 34,000 94,000 62,000 83,000

Michigan-Huron -6,000 53,000 179,000 195,000

Erie -3,000 -10,000 217,000 209,000

Ontario 9,000 8,000 282,000 256,000

Notes: Values (excluding averages) are based on preliminary computations; cfs denotes cubic feet per second. 1 Negative water supply denotes evaporation from lake exceeded runoff from local basin.

2 Does not include diversions.

3 Niagara and St Lawrence rivers average outflows are based on period of record 1900-1989 and 1900-2005, respectively

4 Lakes Erie and Ontario average water supplies based on 1900-1989