Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2013

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2014

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

1952

JUL

1947

AUG

1947

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2015

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

2016

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

2013

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2014

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

2015

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

2016

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

2013

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2014

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

2015

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

2016

JAN

19861936

FEB

19861926

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

602.62183.68602.59183.67603.22

183.86

1952

600.43

183.01

2007

602.13183.53

MichHuron

579.79176.72

579.00

176.48581.99177.39

1986

576.67175.77

1964

579.23176.55

St.

Clair

575.72175.48

575.00

175.26

577.10175.90

1986

572.21174.41

1934

574.64175.15

Erie

572.90

174.62572.08174.37573.95174.94

1986

569.00

173.43

1934

571.69174.25

Ontario

246.42

75.11

245.93

74.96

247.97

75.58

1947

242.78

74.00

1934

245.67

74.88

AUGUST MEAN LAKE LEVELS

(IGLD 1985)

* 2015 Ft.

M.

2014 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2014

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

August 2015

The Great Lakes basin as a whole saw near average precipitation during the month of August. Following a month 

of below average precipitation in July, the Lakes Superior and Michigan-Huron basins received somewhat higher 

August precipitation than average (10% and 5% higher than average, respectively). Lake Erie, on the other hand 

received 14% less precipitation than average during the month of August. Lake Ontario received close to average 

August precipitation. Lake Superior and Lake Michigan-Huron saw above average net basin supplies in August

while Lake Erie and Lake Ontario experienced lower than average net basin supplies. The tables below list August

precipitation and water supply information for all Great Lakes basins.

A comparison of monthly mean lake levels for August to long-term average (1918-2014) shows all lakes at levels 

above long term average August levels. Lakes Superior and Michigan-Huron were 6 and 7 inches above long-term 

August average levels, respectively. Lake St. Clair and Erie were 13 and 15 inches, respectively, above their longterm August averages. Lake Ontario was 9 inches above its August average.

PRECIPITATION (INCHES)

BASIN

August 12-Month Comparison

2015

Average

Diff. % of 

Average

Last 12 

Months

Average

Diff. % of 

(1900-2012) (1900-2012) Average

Superior 3.45 3.15 0.30 110 30.34 30.43 -0.09 100

Michigan-Huron 3.27 3.11 0.16 105 30.34 32.48 -2.14 93

Erie 2.77 3.23 -0.46 86 33.57 35.59 -2.02 94

Ontario 3.05 3.11 -0.06 98 29.64 35.83 -6.19 83

Great Lakes 3.24 3.15 0.09 103 30.53 32.68 -2.15 93

 LAKE

August Net Basin Supplies1(cfs) August Outflows2(cfs)

2015

Average

(1900-2008) 2015

Average3

(1900-2008)

Superior 103,000 94,000 108,000 83,000

Michigan-Huron 62,000 53,000 198,000 195,000

Erie -17,000 -10,000 240,000 209,000

Ontario 5,000 8,000 297,000 256,000

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