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 2016

According to preliminary estimates, the precipitation over all of the lakes for August was above average. Except for 

Lake Superior, all of the lakes were above average by more than 1 inch of rain. The above average precipitation

kept the net basin supplies for all of the lakes above average, except Lake Erie. The larger net basin supplies also 

led to above average outflows for the month of August. The tables below list August precipitation and water supply 

information for the Great Lakes basin.

The monthly mean level of Lake Superior rose from July to August, while the levels of Lakes Michigan-Huron, St. 

Clair, Erie, and Ontario dropped. All of the lakes were above their long-term average (LTA) monthly August levels,

except Lake Ontario. Lakes Superior, Michigan-Huron, St. Clair, and Erie were 7, 11, 12, and 8 inches above their 

LTA levels, respectively. Lake Ontario was 2 inches below its LTA level. In August, Lake Superior was an inch higher 

than it was a year ago and Lake Michigan-Huron was 4 inches above last year’s August level. Lakes St. Clair, Erie, 

and Ontario were all below last year’s August level by 1, 6, and 11 inches, respectively.

PRELIMINARY PRECIPITATION (INCHES)

BASIN

August 12-Month Comparison

2016 Average Diff. % of 

Average

Last 12 

Months

Average Diff. % of 

(1900-2012) (1900-2012) Average

Superior 3.97 3.15 0.82 126 32.37 30.43 1.94 106

Michigan-Huron 4.52 3.11 1.41 145 34.00 32.48 1.52 105

Erie 4.47 3.23 1.24 138 32.83 35.59 -2.76 92

Ontario 4.13 3.11 1.02 133 32.67 35.83 -3.16 91

Great Lakes 4.34 3.15 1.19 138 33.33 32.68 0.65 102

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

2016

Average

(1900-2008) 2016

Average3

(1900-2008)

Superior 101,000 94,000 107,000 83,000

Michigan-Huron 56,000 53,000 207,000 195,000

Erie -11,000 -10,000 222,000 209,000

Ontario 10,000 8,000 260,000 256,000

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

 
Ft.

-1

0

+ 1

+ 2+ 3+ 4+ 5

M.

-0.3

0

+ 0.3

+ 0.6

+ 0.9+ 1.2+ 1.5

2014

SEP

1947

OCT

1945

NOV

1945

DEC

1945

2015

JAN

1946

FEB

1952

MAR

1952

APR

1973

MAY

1973

JUN

1952

JUL

1947

AUG

1947

SEP

19471934

OCT

19451934

NOV

19451934

DEC

19451934

2016

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

2017

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

2014

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2015

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

2016

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

2017

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

2014

SEP

1986

OCT

1986

NOV

1986

DEC

1986

2015

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

2016

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

2017

JAN

19861936

FEB

19861926

CHART DATUM 572.3 FEET (174.4 METERS)

ELEVATIONS REFERENCED TO THE CHART DATUM OF EACH 

Superior

602.69

183.70

602.62183.68603.22

183.86

1952

600.43

183.01

2007

602.13183.53

MichHuron

580.12176.82579.79176.72581.99177.39

1986

576.67175.77

1964

579.23176.55

St.

Clair

575.66175.46

575.72175.48

577.10175.90

1986

572.21174.41

1934

574.64175.15

Erie

572.38

174.46

572.90

174.62573.95174.94

1986

569.00

173.43

1934

571.69174.25

Ontario

245.54

74.84

246.42

75.11

247.97

75.58

1947

242.78

74.00

1934

245.67

74.88

AUGUST MEAN LAKE LEVELS

(IGLD 1985)

* 2016 Ft.

M.

2015 Ft.

M.

** MAX.

Ft.

M.

Yr.

** MIN.

Ft.

M.

Yr.

** AVG. Ft.

M.

* provisional** Average, Maximum and Minimum for period 1918-2015

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).